I had the first version of Parallels, which was a miserable experience. Then they charged full price to move to the second version (which really should have been the first, while the first should have been a free beta).
I learned my lesson. I no longer give my money to companies that treat their customers as beta-testers.
I continue to use Parallels and I was one of the early beta testers as well. You are right, the first couple versions were rough going.
But I have to say, as of version 5, I am able to play games on my VM and forget about dual booting. I specifically use it to play DDO and it works fine.
Part of my solution to the performance problem was going to the new 15" MBP sporting a i7 and 8gb of ram. This thing is a beast. In a good way...