Some users have reported an issue in which Mac OS X 10.6.5 and 10.6.6 show increased kernel panics under normal operating circumstances.
Bad RAM It appears that, in at least some cases, this issue is due to faulty memory modules that operated properly under previous iterations of Mac OS X 10.6.x, but exhibit issues under Mac OS X 10.6.5 and 10.6.6.
This can be tested with a tool such as Rember, which will diagnose and identify memory issues. If the tool finds a problem, try temporarily removing or replacing the module and check for persistence of the kernel panics.
Downgrading to Mac OS X 10.6.4. Although this option eliminates important security fixes included in Mac OS X 10.6.5 and 10.6.6, along with any other enhancements, it may be the best option if a problem is interrupting your workflow.
Reinstall (if you don’t have a current Time Machine backup). Insert your Snow Leopard installation disc, then restart while holding down the C key. When prompted, choose the normal “Install” option. Make sure to select “Preserve Users and Network Settings.”
After installation, you’ll be left with an earlier iteration of Mac OS X 10.6.x (most current retail discs include Mac OS X 10.6.2), but an otherwise largely intact system. Download the Mac OS X v10.6.4 Update (Combo) and apply it if your disc has an earlier version of Snow Leopard. You may need to restore some saved username/password information, browser information, etc.