I think I remember some issues with soundcards and so forth(not as picky as PT, mind you ) IIRC the issue had something to do with midi timing errors. Other nags was about controllers. But its been a while since and the last time I looked, I think they had fixed these issue long ago although some controllers may not play so well (sorry, I'm not entirely sure)!
Overall though, I found the UI very pleasant, it's simplicity is what could actually throw people off the workflow because it's urrrm so very simple lol, but it also has a surprising amount of more advance features which are astounding such as; timing and envelope editing.
And some of the effect plugins are actually pretty darn good. But the big stand-out feature is Melodyne ARA and integrated mastering; being able to switch to mix to make a few adjustments then back to master and it auto-updates.
I'm going to wait for about a year before I decide IF I'll make the switch and purchase the Professional Edition, that along with Melodyne Editor (ARA.) but I'm still concerned about the midi capabilities of S1.2, the prv and the ability to handle large projects containing multiple VI Plugins.
I don't like bounce or freeze anything (midi) = I prefer to keep all midi projects as is (along with backup, copies) this is my preferred workflow and it also allows me to rework, redo, or totally recreate new songs from these midi existing projects.
The community there lacks an OT forum?. I dunno the overall atmosphere seems to lack that causal easy-going chilled out kinda coolness character about it. (Sorry, hard to explain)!