I have a lot of experience with McAfee. My company has a contract with Intel to provide McAfee Livesafe with our services. Is it perfect? No, but it gets the job done well and better than most. That being said their Livesafe product does seem to be better coded and run better than their Anti Virus or Internet Security products. It's also miles ahead of that free version your ISP provides. Certainly better than the free alternatives. I can't tell you the number of times clients have come in, completely infected with malware and they were using Avg, Avira, etc because someone they know swears by it. If your knowledgeable and know what your doing online they aren't bad, but certainly not good for most users.
All that being said, when Intel bought McAfee we starting seeing the once crapware version turn into a much better software. With the latest versions of Livesafe at least, we aren't noticing it using very much memory on most machine. Yes, it will run slow on older machines and low end CPUs but most modern security will do. I have Livesafe installed on 30 plus machines (in addition to client installs) without a performance hit.