I, too, have had very frequent kernel panics since upgrading to 10.7.4. I have an early 2009 iMac 20" (2.66 GHz) with 8G of RAM. I purchased the machine refurbished, and it came with the original 350G HD. I needed more space so I replaced the original drive with a 1.5T Seagate HD.
I tried everything (eliminating non-Apple extensions, reinstalling 7.4 from combo updater, repairing drive, etc.) — nothing eliminated the KPs.
I strongly suspect that it has to do with third-party drives installed as the boot drive. 10.7.4 apparently does not play nice with any internal drives that are not original to the machine, or perhaps it is specific manufacturers (Seagate) that it doesn't like.
My wife uses the iMac extensively for tele-commuting, so it's essential that there be no down time during her work periods.
Anyway I have (painfully) gone back to 10.7.3 (with which I have had no issues) till Apple fixes the problem.
In my case, the memory module is working fine in 10.7.3 but as soon as I upgraded to 10.7.4 kernel panics started to appear. I thought that 10.8 had it fixed but it still gives the same kernel panics. So I'm back at 10.7.3.
An Apple Support Member told me that this is still under investigation.