The main problem with McAfee (and Norton, and most others) is the performance hit they impose. Plus the intrusive nature of the Firewall/Anti-Malware/Anti-Spam/Anti-everything else portions. Plus, all the major players have been reasonably ineffective in preventing and/or catching and removing the really nasty Trojans that have appeared in the last year or so.

Most of the major AV programs started becoming really bloated when they issued new products in response to XP SP2. I'm a longtime Norton user, and their 2006, 2007, and 2008 products slowed computers considerably. They've considerably improved performance with the 2009 Norton AV. I won't go near their Norton Internet Security or Norton 360 versions, however. Users of Trend Micro and AVG have reported serious performance problems in the last 2 years, also.

McAfee has always had the reputation of being worse than Norton in exacting a performance hit. This may not have been true in 2007 and 2008. Eset's NOD32 is highly streamlined compared to Norton or McAfee. Several other products impose very light performance penalties, but you need to study the reviews to find out if they are effective, take forever to scan, or have other issues. Interestingly, many of the best AV products come from Russia and Eastern Europe - also the place many of the viruses come from.

Best advice to avoid performance problems -

- buy an antivirus program that specializes in viruses and is still fast. ESET's Nod32 is good, Norton 2009 isn't bad. Kaspersky's not bad.
- if you use McAfee or Norton on a desktop behind a hardware firewall, turn off any internet protection (firewall) features.
- turn off anti-malware features and use a trio of ad-aware/spybot S&D/malwarebytes on an occasional basis (twice a month is plenty once the machine is clean).
- turn off anti-spam. If you have spam problems, a) get a better ISP, 2) a better mail client, 3) 3rd party anti-spam programs.