I'm seeing the same problem - left mouse button either "sticks" on pressed or won't press.
I have a 15", late 2008 MBP with a wired external keyboard and a bluetooth mighty mouse (model A1197). I've seen that other folks attribute this problem more w/ a bluetooth issue than anything else.
Funny thing is that for me, it didn't happen until I updated to OS X 10.7.3. Not on 10.7 or 10.7.2. Go figure.
I use my MBP 8-12 hours per day. The left-button lock-up seems to resolve itself for some period of hours after a reboot - which I end up doing 2-3 times per day. When the left button on the mouse misbehaives, the MBP trackpad exhibits the same behavior. the keyboard still works fine, so I often end up using as many keyboard short cuts as I know to try to shut stuff down, and have to occasionally resort to the press-n-hold of the power button to reboot.
The boards are covered with anecdotal fixes and I'm currently at a loss to find a root cause or official Apple solution. I'm reluctant to downgrade back to OS X 10.6 or to revert my mouse bluetooth drivers back to the stable (pre-10.7.3) versions.