I used to use Cinema4D XL 7 quite a bit, even made a 5 minute animation with it. (and my Tar, among other things--
iboing anyone? ) I liked using it and it taught me the basics, but I use Maya almost exclusively now.
As far as how to learn.......Im the hands on type. Try stuff, break it, read the book, fix it. No special site or tutorial.
Some things I liked about Cinema 4D:
-Modeling is a snap (all polys though, no real Nurb manipulation)
-Hyper Nurbs, the best Sub-D out there IMHO
-Simplicity and easiness of the renderer, which is nice and clean (yet less powerful than others) Sure beats the Maya renderer!

-Dynamics and Particles (they are just so damn easy!)
Some things I hate about Cinema4D (XL7)
-Character Setup (Maya whoops its ass)
-Keyframing and Animation UI (again, so much more user-friendly in Maya)
-Lighting (cant beat IPR in Maya)
-Overall UI and interface. (the 3 button mouse in Maya is indespensible)
-Graph editor (or whatever its called in C4D) Just not friendly or fast.
- No Nurbs surface editing/modeling! Hello???
I know C4D 8 is supposed to be much more advanced and 'Maya-like' but I havent touched it.
Anyway, I could go on for a while but I gotta get back to work
