It's really hard to judge since every phone acts so differently with 3rd party apps :( what could leak for me may not for you or the next person and vice versa.
Printable View
the issue is the databases they create, and how the device and the apps interact with removing old/unused databases...
during "uptime events" (time between battery pulls) the reaction of an OS to an app can vary quite drastically. sometimes i'll do a battery pull to refresh everything, especially if i'm helping someone test a theme or a hybrid, etc. and i'll have no memory leak for like a week, then i'll reset and i'll crash from no memory available when trying to BBM or something...
go read the thread on CB about resolved memory leak and see what you think.