I recently posted some data about applications taking up the most RAM on my laptop. That was after 9 days of uptime, while this is after 12 hours:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 16033 root 20 0 527m 109m 11m S 3 5.5 6:52.82 Xorg 17834 mg 20 0 244m 105m 24m S 6 5.3 3:26.49 firefox 26425 mg 20 0 96872 58m 12m S 0 2.9 0:01.71 evince 16747 mg 20 0 90704 54m 19m S 0 2.8 0:10.70 tomboy 27169 mg 20 0 166m 53m 23m S 0 2.7 0:07.05 banshee-1 27167 mg 20 0 77392 31m 17m S 0 1.6 0:01.16 pidgin 16706 mg 20 0 86508 27m 18m S 0 1.4 0:35.35 gnome-panel 16708 mg 20 0 75196 20m 14m S 0 1.0 0:02.80 nautilus 20092 mg 20 0 61880 19m 11m S 1 1.0 0:07.08 gnome-terminal 16614 mg 20 0 58456 15m 9836 S 0 0.8 0:09.82 gnome-settings-
I don't have GNOME Do any more, and I've only one of the two PDFs open in Evince. I don't see multiload-applet on the first page of top output, which seems to indicate a slow leak. Evince has the same two documents. That concept doesn't quite apply to Banshee or Pidgin, but Pidgin's numbers are quite striking anyway (from 70 megs VIRT to 1.6 gigs VIRT in 9 days; thankfully RES only grows 2x during that time).
OS: Ubuntu 8.10, up-to-date with all the updates from -security, -updates, -proposed-updates and -backports.
Incidentally, I have 12 hours of uptime because my battery died while the laptops was suspended during my flight back home (either that, or it work up in the backpack, which is a scary thought). Apparently Ubuntu tried to hibernate when the battery was very low, which was a nice gesture. This didn't work out so well when resuming, since the kernels didn't match -- I had installed a kernel update, but hadn't rebooted. I don't think I ever used hibernation successfully in Linux.