Symantec Corporate Edition was pretty much hassle free. It didn't take a whole lot of resources from the server/management end, and didn't bog down the clients with a light weight software foot print.

Along came Symantec Endpoint Protection shortly after Vista was released. The first reports was that it the included firewall component and locking off server, and bogging down computers.

You can read a long history of the buggy-ness of SEP 11 at the Symantec Forums - http://www.symantec.com/connect/security/forums/endpoint-protection

What I have ended up doing, resulting in a reliable install, is to follow this points:

• Had success with a Windows 2003 32bit Server for SEP Management Server role - at least 1 gig of memory (I do have it running on an old management server at a clients with 512meg ram - but it is slow)
• Setup Client Install Feature Set - ONLY include Antivirus and Antispyware Protection
  • Most of my clients do email virus scanning before it hits their email server
  • DO NOT install Network Threat Protection AND Proactive Threat Protection
• Setup Policies
  • make sure any scheduled scans happen after hours
  • do not enable start up scans (this kills computers on start up)
  • make sure that Missed Scheduled Scans is not selected
  • I usually set delete threats
• For laptops - I will set up a different LiveUpdate Policy to allow
  • User the default management server
  • AND Use a LiveUpdate server - this allows users to update when they are on the road

The point of this is to optimize SEP11 settings for the best performance. With everything enabled, it runs like a dog, and so far, the protection with the minimal setup options provided above are sufficient.