I've been using harmony remote basically from day 1 - had original ez-zapper, then two 768s and 720. I've recently switched to MX-1200, after having negative experience with 2 900s:

First one would lock up after the update - just sit there with white screen until I pulled the battery. Exchanged it, helped with that particular issue. But both had a different issue - they would randomly loose RF connection. It would reconnect in a sec but by that point macros would get screwed up. And the biggest problem both of them had - I'd turn on TV, start watching and then a few minutes later, when I wanted to pause or change volume, the remote didn't respond. If I went and changed to IR from RF, it would start controlling. Then it would start working again, with RF, as mysteriously, as it stopped.

Now, I do not believe remotes were defective, perhaps something in my environment interfered with RF. But, I couldn't get it working and tech support was of no help.

I have since upgraded to MX-1200 (with MRF-350) and couldn't be happier. Yes, it's much more expensive, but for the first time control is rock solid. RF reception is great 100% of the time. There are tons of graphics images available and I can add my own (although it's a bit of a hack). And the biggest plus for me - with URC you can change number of IR signals sent with each key press. I could never figure out why harmony remotes were as responsive with Tivo as the original one. But with URC, I've increased repeats to 5 and it works perfect.

Now, I'm not bashing 900. I really like it and really wanted to keep it and not spend 3x the money. If it works for you - great. Just didn't work out for me.

P.S. One thing to consider (and it's been talked about endlessly) is that 900 doesn't have macros. So in case of X10 controller, you would need to have separate buttons for devices and on/off. I do not believe you can have one button sending Unit Code and On/Off command. If you have modified all house IR-543, it's even worse because that one needs House Code as well. I've switched to Insteon IR controller so that wasn't an issue for me.