I was a Cakewalk user, and then Sonar, dating back to the Windows 3.1 days when it was purely Midi. When I finally moved to Cubase I kept Cakewalk installed for quite a while as a safety net. This was in the 32 bit days, but I never had any problems with Cakewalk plugins not running well in Cubase.
There was a learning curve to be sure, but it was actually pretty easy for me to get going and be productive again. A lot of the basic recording and mixing stuff is pretty obvious in both environments, and the manual is well written for those “how do I do X?” moments (which I encounter no matter what software I use).
I’ve been through PT, Cakewalk / CW Pro Audio / Sonar, Logic, Nuendo, Cubase and I think a couple of others. I work in Windows (and thus got kicked to the curb when Apple bought Logic) and have found Cubase to be everything I need as well as being much, much more stable than Sonar ever was. Of course, no software is perfect so that latter statement varies from user to user depending on your environment. That said, there isn’t anything I had in Sonar but found lacking in Cubase, so hopefully those making the transition will have a good experience as well.