Seems stable now
I got a free trial a while back to see how it worked. At first, I wasn't too impressed.. the apps are good etc., but nothing I thought I really needed, and the push service didn't work with my iphone at all (I have it without contract, and without any data plan, but it's usually connected via wifi).
The push service was fixed a few days later though, and works very well. The idisk is immensely handy, and the other web apps are pretty useful if you want to look up a contact or check your diary while out somewhere. I'm pretty tempted to pay for it now, so I guess they got something right.