Since upgrading my Mac Book Pro (15 inch, mid 2010 with Intel i5 processor) from Snow Leopard to Lion I had been experiencing some strange behaviors (like the screen saver popping up unexpectedly while working) and, what matters most to me, serious performance issues.
Regarding the screen saver, it seems to be due to an incompatibility between my Mac Book Pro model and Lion. Some other people claim it is related to AirPlay being installed. Uninstalling AirPlay or disabling the screen-saver solves the problem. As a side effect, Skype believes the computer is constantly idle and turns the online icon to away (a setting in Skype solves the problem and puts you always online). Another strange behavior is the screen-saver starting at the login screen. There seems to be no solution for this problems in particular. Hopefully Apple will soon release a fix.
Now to the performance problems: I have been experiencing continuous slow downs to the point of having to wait tens of seconds for tasks to complete and applications to come back to life. The Activity Monitor showed all the RAM being used and massive Swap Files.
Looking on the Internet there are many mentioned causes and related solutions. None worked for me, until I got an hint from a person describing a solution to a similar problem. At the end of the day, the problem seems to be caused by old drivers and helper applications that, while working perfectly with Snow Leopard, are causing issues to Lion. Unfortunately these applications are not checked or removed during the upgrade process and they are left in the system causing troubles.
The one that was definitely “killing” my Mac turned out to be Flip4Mac. Flip4Mac allows to play Windows Media format files on the Mac. If it is installed, it can be found in the System Preferences under Other (usually at the bottom). Flip4Mac can be uninstalled through a script that is distributed with the application.
Once I uninstalled Flip4Mac and rebooted, my Mac Book Pro seems even faster than with Snow Leopard! 🙂
Final note: even if you don’t have Flip4Mac, other similar drivers or extensions, leftovers from the Snow Leopard install, may be causing issues to Lion. You may want to uninstall them all and install newer versions. A clean install of Lion will definitely solve the problem though. I have not yet checked whether a newer version of Flip4Mac, compatible with Lion, exists. I am just enjoying my fast Mac Book Pro with Lion at the moment!