The way I tend to approach the feature set is very rarely to sit down to learn any particular thing. It's more that I just get on with what I'm doing, and from time to time, I'll run into something I need to do, so I'll have a poke around the help files and the forum to see if there's a way. And the more developed and mature Sonar becomes, the more rare it is that I can't do whatever has come up directly in Sonar.
For example, we've had the vocal alignment thingy for nine months now, and I only first used it about two months ago. I was working on some vocal comps with a singer, and he said, literally, "is there a way of tightening up the doubles, like a vocal alignment thingy". And I thought, ah, there is! And it turned out to be totally easy to use, and solved our problem right away.
Another example would be that I'd not given any thought at all to the addition of new export formats this year, and then I was doing a sound effects job recently, where they needed all the files in Ogg Vorbis format, and I thought, ah, great, they added that to Sonar, didn't they? Saved me having to have a post-export conversion process.
I think that's what I particularly like about Sonar. All the well-known DAWs are good at lots of things, and some of them are especially good at a few things, but for my money, Sonar is the most
comprehensive. Whether that matters to you will depend greatly on the kind of work you're doing with the program. Myself, I'm doing all kinds of stuff; band production, mixing, remixing, audiobook production, sound effects, all kinds. Whatever comes in that'll pay the rent, basically. And I very rarely have to go outside of Sonar (and its bundled instruments, effects and tools) to get anything done. Which is pretty impressive, I think.