I’ve been using Cakewalk products for years and upgraded throughout that time. I’m currently on Sonar X1 Producer – Expanded. After many months on X1 I really think they blew it with the new interface. I still prefer 8.5 better and I thought it was much more intuitive. Just my 2 pennies worth.
I went to X1 (Studio) when it came out and it took me a while to get comfortable with it. Using SonarPlus to get rid of the MultiDock really helped me. Some people like it, but to me it was a nuisance. The Scott Garrigus book has also made my life a bit easier.
Recently I opened 8.5 for the first time since upgrading and I was surprised by how cluttered it looked to me. Now that I’m used to X1 I’m happy with it. My own 2 cents.
Some X1 Producer features I'm glad I learned more about are Track Templates, Screen Sets, AudioSnap and the Browser. It's funny, I got a big project with a client right afterward and the time I had recently put into studying X1 and Sound Forge really paid off!