The biggie missing in RB for me is Loop Record for comping vocals (singing sections of a song multiple times and have each take automatically put on a different track without me having to stop and rewind after each one). It's a feature I expect in any sequencer these days and something I absolutely need more than any of the existing RB features.
I need to sing a portion of a song through a couple of times before I get into it so, when working in Logic, I would go into Loop Record and sing half a dozen takes of a song section in one go then have them automatically put on separate tracks. I'd like to be able to easily select the best portions then combine them into a single lead vocal track.

I regard this as a really basic and essential function - I had it on simple Atari sequencers in the 1980s. RB has really powerful features yet lacks this elementary one - unless it's there and I'm missing it somewhere (and PG tech support have missed it too)?

I no longer have access to my expensive version of Logic Platinum since Apple bought the company and they stopped supporting it on PC so it's stuck on my old P3 with Windows 98. I use RB on my new Windows Vista laptop and am now having to contemplate buying Sonar just so I can get Loop Record.

But if RB was to include Loop Record...

Don't know if PT had it? I have PT but could never get it to work.

RB often crashes when I press the Stop button. But that's another story...

Frankly, I would not waste my money on Sonar. I have producer 8 issues in Vista. My Rapture synth for Sonar, sold by Cakewalk and touted as totally Vista compatible won't even run. I have been with them for some time but each issue seems to have more config issues than the former. And as a Roland user of several devices, we all know they make the best gear and worst manuals on the planet--and now Cakewalk is Roland.
And the email support is ridiculous. You have to submit a complete new form each time instead of entering into a back and forth dialogue with the support tech--and forget the phone.