While I don't own one, I've ridden one of their MTBs extensively and know quite a lot of people that have their bikes.
About the road bikes I can say that I don't know anyone at all who didn't like his or hers, if it fits. Their geometry is usally really relaxed.
We've got a really good sprinter in our club who raced his very successfully. He also broke one in a crash, but that can happen.
I really think they make good bikes.
That being said, the customer service or buying experience I've heard everything from very pleased and buying various more to people who wanted to blow up their headquarters and did have their lawyers do the correspondence in the end. They've recommended or just sent out wrong sizes or forgotten about entire orders and it can be really difficult to get through to them, especially in the spring. I'd like to give you an idea of what your odds are, but I've really no basis to do this on. I've got a feeling it's a little worse than in the LBS, but I could be wrong. What's true though is that if something goes wrong, it's a lot more annoying than having to walk back out of an LBS.
I don't know if that is still up to date, but a couple of seasons ago they had this campaign advertising their perfect fit program and at the same time you couldn't get a different crank length than they decided would be best with a certain frame size and to get a different stem length you had to pay full retail. You couldn't use your own one either, as they had a 1.1/4 steerer. That really annoyed the heck out of me, but I'm a little strange in that regard.
What that brings me to though, is that I'd recommend looking at the bike you get and the price you pay for it carefully. You have to add the price for the bike, then they make you buy a box, pay the shipping and maybe the price for a stem swap.
Then a LBS will often give you a very solid discount or even a free check up after a while.
A lot of times you will still get a bike with very good value, but the price you first see on their website can be misleading.
I'd also say that having a decent idea of how to take care of your bike and the proper tools to do so, or knowing someone who does, is very helpful when mail-ordering a bike.
About the holding up on rough roads I wouldn't be too concerned, but you could search the web for what Omega Pharma Lotto used in the spring last season. I know some, if not all of their riders used the aluminium frame, but that could have been due to fitting issues, too.
Hope that helped.
"Nothing compares to the simple pleasures of a bike ride," said John F. Kennedy, a man who had the pleasure of Marilyn Monroe.