tix 2.7.3, online for over 7 hours and stays at 3.4 GB RAM once reached its steady-state (don't wonder, I have Channels enabled (all of them, and they're heavy!), tons of transfers and logging).
Out of memory!
nothing to do with memory.
Why so... s-sure? I told you to inspect the processes with Process Explorer to help narrow it down, Task Manager is not as specific as PE. New uTorrent is a very good example of 'new bloat', it needs 400MB of memory just after startup and a fresh install.
after that firefox with addon "group speed dial" works incorrect - the new tabs crashes.
You are lucky your PC doesn't freeze as it would try to use the pagefile (or maybe there's none in your case :)