I've been using a Line 6 M9 for the last month and am very happy with it.
Main reason I wanted to try it was for the modulation/delays. I never liked any one phaser or delay enough to be able to only have one on my board. Now with the M9, I have access to dozens of phasers, flangers, delays and reverbs. If I were to put one of each on my board, I would easily spend more than the M9 costs and I wouldn't have much flexibility.
What I didn't think I would have much use for were the fuzzes and the overdrives. Some of them do sound very digital...on the other hand, some of them have turned out to sound really freaking awesome. More importantly, live, no one would really be able to tell.
I am still going to keep a dedicated fuzz and O/D on my board, because I have a couple that I really like, but so far I've been able to do a lot of tasteful additions to my bands songs with the M9. I run mine before the input.
Oh and not to forget to mention that it has a pretty kickass looper built in as well.