This is under GNOME 2.32.0 and stock Fedora 14 with all current updates applied.

gnome-terminal or perhaps gnome-pty-helper doesn't relinquish pty's until you close the last terminal.

i.e

Start gnome-terminal and open three tabs, these are assigned /dev/pts/{0,1,2}

Close the middle tab pts/1 and we still have a /dev/pts/1 entry

Open another tab and it gets assigned /dev/pts/3 (should have been pts/1)

Exit gnome-terminal altogether and its /dev/pts entries are gone.

ssh logins and xterm's both properly close the pty and allow them for immediate reuse.

On my workstation I currently have the following in /dev/pts

$ ls /dev/pts
0   11  14  17  2   22  25  28  30  33  36  4   5  8
1   12  15  18  20  23  26  29  31  34  38  40  6  9
10  13  16  19  21  24  27  3   32  35  39  41  7  ptmx

But only actually have 7 terminals open.