I notice a drop but not as severe as yours. Mine drops 8-10 MB running UT. You may want to tweak your configs - refresh rate, etc. for optimum performance. Apps like UT that run in the background drain memory pretty bad.
I notice a memory drop on my Storm, but not nearly as severe as yours. most of the apps that we run, don't run in the back ground when we close them. the ones that do use memory constantly, being that they are open in the background, than those that close.
I was in the process of narrowing it down. Between my weather app and UT, I wasn't sure which one was causing more "damage". BUT, with BBM5, does it really matter??? LOL. I'm charging at 5PM if not sooner now. I was able to go 'til 10/10:30PM before I even thought about plugging in.