Well, I've been an Ocelot user for many years (am I the only one here? ), but haven't yet used an ISY. I do look forward to it, though, and will certainly be able to provide a lot more comparison information when I have.
ISY and Ocelot are, I think, not so much competitors as complementary, so I'd really like to approach it from that perspective. I think they would make an excellent combination.