We have been running Symantec for years, and are in the process of switching to a new product. SAV 10 had many flaws, SEP11 is terribly bloated, unreliable, complex, and causing many problems for other programs.
It looks as though we will be switching to MS Forefront. Have a trial setup in 2 schools, very impressed so far. Workstations are much faster at everything with Forefront (compared to Symantec), and users at those schools have noticed the huge difference and are very pleased.
As well, I really like the way it integrates with our existing technologies (AD, policy management, WSUS). Price is fantastic too.