As a BT customer, I get "free" McAfee for up to 5 machines. I am not very good at this techie stuff. In the past, I have loaded McA sort of automatically. There have been two occasions in the last couple of months where I have got rid of it.
Once - described on another thread - McAfee interfered with Windoze updates on a Vista machine. No idea why. Removing McAfee and installing Security Essential seemed to solve the problem.
Second case was a wheezing old pc with XP SP3. it appeared to be slower and slower. Removal of McA and installing Sec Ess helped it increase its speed.
On my much newer, all singing 7/64, I just never put McA on. Just secEss.
So in my customer experience, nothing wrong with McA, but the time might come to dump it some time in the future.