I'd say, not bad. I've had a replayTV for a while now (still use it of course, mostly for the kids' stuff, then offload using dvarchive). I have 2 FiOS dvrs. i like the fios dvr much better than my prior on Scientific atlanta w/ cablevision.
With FiOS, you've got 30 sec skip, all resume points are saved, shows are grouped together.
You don't think you have 'channels' like with replaytv (and Tivo) i think were it will record say anything 'sci-fi' or any show with 'power rangers' in the title. also, I think the searching ability is a bit rudementary.