I'm just browsing their website and it seems a bit too good to be true... The only drawback I see are daily sending limits (which I'm very happy with).
I've been using them for 2 years now, I'm a big fan of the service. I thought it was a bit too good to be true at first but I was slowly transitioning from a gmail address to my own domain so it wasn't a huge issue if it fell over or something. Turns out to be pretty rock solid and I'm a very happy customer now.
