I'm coming across (and hearing from) a number of disgruntled Mac OS X 10.7 'Lion' who are experiencing problems with Apple's latest OS release.
Four separate problems stand out:
Random crashing that results in a totally black screen
Once the system crashes, it's a hard reset time.
There's no solution from Apple yet but it seems that the problem here is down to NVIDIA drivers and forcing the system to use integrated graphics only using a third-party tool (gfxCardStatus) helps alleviate the problem.
[A tipster has emailed in a possible solution - Navigate to ~/Library/Preferences/ByHost/ (hidden by default, go to it by opening the Go menu in Finder, hold down the Option key and paste the full path above in Go To Folder) and delete all files that containing "windowserver" and then reboot the Mac. This process will need to be repeated if you hook your Mac to an external monitor.]
This is annoying (I'm seeing this happen, although not often). Basically the WiFi connection drops and the only way to get it back working is to switch the WiFi adapter off and then back on again.
A temporary solution to this is to create a script that pings periodically.
Poor MacBook Pro battery life
Installing Lion causes a significant drop in battery life.
This might be related to the fact that Lion doesn't terminate application processes immediately when applications are closed or it could be a graphics driver issue not allowing the system to switch to integrated graphics from discrete graphics (again, gfxCardStatus might be useful).
Viewing videos crash causes freezing on new iMacs
All video types appear to cause the freeze - Flash, H.264, QuickTime, AVIs, MKVs, YouTube ...
This is another issue that could be related to graphics card drivers ... but perhaps not.
Some of these issues were being talked about when developer releases of Lion were made available, so it seems like some bugs slipped though the net.
If you're affected by these bugs, your best bet is to wait for a patch from Apple. If you're thinking about upgrading and problems like this would be show-stoppers for you, then you might want to wait until Apple releases a patch.
If you're a Lion users, have you had any of the above problems (or something else)? Let me know in the TalkBack!