I haven't tried Premiere 6.5 yet, but I've used Premiere 4, 5, and 6 for 7 years. For the money, Premiere is a great editing program. Definitely much more powerful and robust that iMovie. iMovie is easier to use, but you run into its limitations very quickly. If you can afford it and need more than what iMovie offers, Premiere is a good buy.
If you're willing to spend more money, Final Cut Pro is the way to go. I switched from Premiere to FCP about a year ago, and I haven't looked back. It's a very powerful editor, has some great real-time effects, and just enough compositing features to get by. And I prefer FCP's interface over other editing applications. It just feels right to me (completely personal preference).