I just built Gnome-shell using jhbuild and managed to get it going.
Unfortunately it crashes on me under certain, repeatable conditions.

Steps to reproduce:
1. Before starting the shell have four applications open (Google Chrome, Spotify, Thunderbird and gnome-terminal).
2. Start gnome shell (./gnome-shell --replace)
3. Open the overlay (clicking Activities, hot corner or Meta-key)
4. Hover over any of the open applications windows.

Expected result: Not sure, long since I tried the shell :)

Actual result: Crash back to metacity with the following log messages:

----- BEGIN console output -----------------

Gtk-Message: Failed to load module "canberra-gtk-module": libcanberra-gtk-module.so: kan inte öppna delad objektfil: Filen eller katalogen finns inte
Fönsterhanterarvarning: Log level 16: Accessibility: org.a11y.atspi schema not found. Are you sure that at-spi or at-spi2 is installed on your system?
Fönsterhanterarvarning: Log level 16: Accessibility: invalid module path (NULL)
Fönsterhanterarvarning: Log level 16: Accessibility: error loading the atk-bridge. Although the accessibility on the system is enabled and clutter accessibility is also enabled, accessibility support on GNOME Shell will not work
    JS ERROR: !!!   WARNING: 'anonymous function does not always return a value'
    JS ERROR: !!!   WARNING: file '/home/ho/gnome-shell/source/gnome-shell/js/ui/overview.js' line 233 exception 0 number 157
Panel leaving: a new panel shell is starting.

(gnome-panel:26405): EggSMClient-CRITICAL **: egg_sm_client_set_mode: assertion `global_client == NULL || global_client_mode == EGG_SM_CLIENT_MODE_DISABLED' failed

(gnome-power-manager:25501): Gtk-WARNING **: GtkImage 0xabc030 is mapped but visible=1 child_visible=1 parent GtkTrayIcon 0xab8000 mapped=0
      JS LOG: GNOME Shell started at Thu Jan 20 2011 16:58:16 GMT+0100 (CET)

(mutter:26529): GdmUser-WARNING **: Unable to load CK history: no seat-id found

** (ck-history:26543): WARNING **: Unknown option --since=2010-11-21T15:58:17.085026Z
radeonSetSpanFunctions: bad format: 0x0002
radeonSetSpanFunctions: bad format: 0x0002

(gnome-power-manager:25501): Gtk-WARNING **: GtkImage 0xabc030 is mapped but visible=1 child_visible=1 parent GtkTrayIcon 0xab8000 mapped=0
Shell killed with signal 11

----- END console output --------------------------

The output from glxinfo is:

----- BEGIN glxinfo output -------------------------
name of display: :0.0
display: :0  screen: 0
direct rendering: Yes
server glx vendor string: SGI
server glx version string: 1.4
server glx extensions:
    GLX_ARB_multisample, GLX_EXT_import_context, GLX_EXT_texture_from_pixmap, 
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, 
    GLX_OML_swap_method, GLX_SGI_make_current_read, GLX_SGI_swap_control, 
    GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, 
    GLX_SGIX_visual_select_group, GLX_INTEL_swap_event
client glx vendor string: Mesa Project and SGI
client glx version string: 1.4
client glx extensions:
    GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context, 
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, 
    GLX_MESA_swap_control, GLX_OML_swap_method, GLX_OML_sync_control, 
    GLX_SGI_make_current_read, GLX_SGI_swap_control, GLX_SGI_video_sync, 
    GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, 
    GLX_SGIX_visual_select_group, GLX_EXT_texture_from_pixmap, 
    GLX_INTEL_swap_event
GLX version: 1.4
GLX extensions:
    GLX_ARB_get_proc_address, GLX_ARB_multisample, GLX_EXT_import_context, 
    GLX_EXT_visual_info, GLX_EXT_visual_rating, GLX_MESA_copy_sub_buffer, 
    GLX_MESA_swap_control, GLX_OML_swap_method, GLX_OML_sync_control, 
    GLX_SGI_make_current_read, GLX_SGI_swap_control, GLX_SGI_video_sync, 
    GLX_SGIS_multisample, GLX_SGIX_fbconfig, GLX_SGIX_pbuffer, 
    GLX_SGIX_visual_select_group, GLX_EXT_texture_from_pixmap, 
    GLX_INTEL_swap_event
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: Mesa DRI R600 (RS880 9710) 20090101  TCL DRI2
OpenGL version string: 2.1 Mesa 7.9-devel
OpenGL shading language version string: 1.20
OpenGL extensions:
    GL_ARB_depth_clamp, GL_ARB_depth_texture, GL_ARB_draw_buffers, 
    GL_ARB_draw_elements_base_vertex, GL_ARB_fragment_program, 
    GL_ARB_fragment_program_shadow, GL_ARB_fragment_shader, GL_ARB_imaging, 
    GL_ARB_multisample, GL_ARB_multitexture, GL_ARB_occlusion_query, 
    GL_ARB_pixel_buffer_object, GL_ARB_point_parameters, GL_ARB_point_sprite, 
    GL_ARB_provoking_vertex, GL_ARB_shader_objects, 
    GL_ARB_shading_language_100, GL_ARB_shadow, GL_ARB_shadow_ambient, 
    GL_ARB_texture_border_clamp, GL_ARB_texture_compression, 
    GL_ARB_texture_cube_map, GL_ARB_texture_env_add, 
    GL_ARB_texture_env_combine, GL_ARB_texture_env_crossbar, 
    GL_ARB_texture_env_dot3, GL_MESAX_texture_float, 
    GL_ARB_texture_mirrored_repeat, GL_ARB_texture_non_power_of_two, 
    GL_ARB_texture_rectangle, GL_ARB_transpose_matrix, 
    GL_ARB_vertex_array_bgra, GL_ARB_vertex_buffer_object, 
    GL_ARB_vertex_program, GL_ARB_vertex_shader, GL_ARB_window_pos, 
    GL_EXT_abgr, GL_EXT_bgra, GL_EXT_blend_color, 
    GL_EXT_blend_equation_separate, GL_EXT_blend_func_separate, 
    GL_EXT_blend_logic_op, GL_EXT_blend_minmax, GL_EXT_blend_subtract, 
    GL_EXT_compiled_vertex_array, GL_EXT_convolution, GL_EXT_copy_texture, 
    GL_EXT_draw_range_elements, GL_EXT_framebuffer_object, GL_EXT_fog_coord, 
    GL_EXT_gpu_program_parameters, GL_EXT_histogram, GL_EXT_multi_draw_arrays, 
    GL_EXT_packed_depth_stencil, GL_EXT_packed_pixels, 
    GL_EXT_pixel_buffer_object, GL_EXT_point_parameters, 
    GL_EXT_polygon_offset, GL_EXT_provoking_vertex, GL_EXT_rescale_normal, 
    GL_EXT_secondary_color, GL_EXT_separate_specular_color, 
    GL_EXT_shadow_funcs, GL_EXT_stencil_two_side, GL_EXT_stencil_wrap, 
    GL_EXT_subtexture, GL_EXT_texture, GL_EXT_texture3D, 
    GL_EXT_texture_cube_map, GL_EXT_texture_edge_clamp, 
    GL_EXT_texture_env_add, GL_EXT_texture_env_combine, 
    GL_EXT_texture_env_dot3, GL_EXT_texture_filter_anisotropic, 
    GL_EXT_texture_lod_bias, GL_EXT_texture_mirror_clamp, 
    GL_EXT_texture_object, GL_EXT_texture_rectangle, GL_EXT_texture_sRGB, 
    GL_EXT_vertex_array, GL_EXT_vertex_array_bgra, GL_APPLE_packed_pixels, 
    GL_ATI_blend_equation_separate, GL_ATI_texture_env_combine3, 
    GL_ATI_texture_mirror_once, GL_ATI_separate_stencil, 
    GL_IBM_multimode_draw_arrays, GL_IBM_rasterpos_clip, 
    GL_IBM_texture_mirrored_repeat, GL_INGR_blend_func_separate, 
    GL_MESA_pack_invert, GL_MESA_ycbcr_texture, GL_MESA_window_pos, 
    GL_NV_blend_square, GL_NV_depth_clamp, GL_NV_light_max_exponent, 
    GL_NV_packed_depth_stencil, GL_NV_texgen_reflection, 
    GL_NV_texture_rectangle, GL_NV_vertex_program, GL_OES_read_format, 
    GL_SGI_color_matrix, GL_SGI_color_table, GL_SGIS_generate_mipmap, 
    GL_SGIS_texture_border_clamp, GL_SGIS_texture_edge_clamp, 
    GL_SGIS_texture_lod, GL_SUN_multi_draw_arrays

----- END glxinfo output -----------------------------------------