Hmm...I currently have 7 windows, 9 sites, and 45 tabs open, and with all that it just hit a bit over 90MB of RAM...

EDIT: And just closed all but this window with 4 tabs and the usage went down to about 65MB.

Seems very strange that it would cause storage leaks.

EDIT2: Seems the 1.5.0.1 fixes a few known storage leaks. (I'm still running 1.5.0.0)