Are you using it in a 'Seven Circles' way like de la Maza recommends in his 400 points in 400 days routine (basically doing all the problems in shorter and shorter stages until you sit down for ~8 hours one day and do them all)?

I've seen it get good reviews elsewhere, as well. There is an old post on the blog "Confessions of a Chess Novice" looking at various software packages for use in a Seven Circles way.

I'm considering getting it, but there are a few other things I'm looking at right now (books and other software).