Alt+middle anywhere on the window will resize it, and you can 
resize by clicking the bottom edge of the titlebar with left mouse. 
Will be changing to top edge.

WONTFIX, then, Havoc?

I also missed this feature from Nautilus as it's IMO the most
convenient way to resize a window with the mouse. Those small borders
are usually too small and not every window has a resize handle.
Pressing ALT is not very convenient.
I would much prefer if every resizable window would just have a
decently large and visually separated resize handle. This is probably
part of the theme and I'm wondering why this isn't more popular among
theme authors. I did something like this in one of my themes and found
it to be very convenient. You can see it here:
http://62.26.209.204/download/amadeus/Amadeus-Screen.png
Notice the blue edges in the bottom left and right and the large
bottom border which makes windowing a pleasure. :)

Oopse, I got a little bit carried away here... I guess what I want to
say is that it's not important to implement the
middlemousebutton-on-title-resizing but if it isn't, resizing should
be made a little bit more convenient (and hopefully more intuitive)
IMHO. Maybe just creating a defaulttheme with nice resize-handles
would solve this.

*** This bug has been marked as a duplicate of 90418 ***