On a Mac it works pretty well - still some annoyances but it's a thousand times better than the PC version which began as a half decent bit of software and rapidly descended into a bloated mess.
One minor annoyance, that Apple in fairness did sort out after much emailing, was d/l tracks via itunes on the iphone, iTunes on the MacBook wouldn't recognise them and sync them over and when I upgarded to OS4 it 'lost' some albums and random tracks on the phone and I didn't have them backed up on the Macbook. Even Apple couldn't explain why...and eventually gave me a free dowload of the material.
In fairness one album was Vamprie Weekend so it wasn't about the music...more the principle