Toontrack EZ Keys - Tell me about it.

Basically, yes. I have it, and have used it on a couple of things . The big problem is that the patterns seldom fit with the spaces in the songs I write. You know how a good keyboard player finds the space for their part? Hard to make that happen in my stuff. People usually build tracks up from th e drums, so using a premade drum pattern, you work parts around it. Maybe if I did drums, then EZ Keys, things would go better, but since I do drums/guitars/bass it has not worked well for the most part. That said, the instruments sound great and th e patterns sound real.

I use it
it works great for finishing a progression(by trial and error of sounding different chords)
I stay away from Inserting chords. (find it Then play it).
If you follow the DAW Meter. Then pattern timing is OK.
Putting in a progression and getting lost with the changes and patterns. Is One of the Coolest things about it Though.
I have come up with some really nice pieces of music that way.
Use it in your DAW. Drag the midi. And Forget about Their sounds.

I have EZkeys and EZdrummer, I bought them both a quick building blocks, for which later I'd replace with my own recorded performances. They work great as part of my workflow.

EZdrummer I use for quick drum backing track patterns, while EZkeys I use more for it's samples than the patterns, and playing my own parts. However, EZkeys' patterns are a great way to identify some stylized keys licks and roll your own from there. 

Back to EZdrummer- The song creator function is so brilliant, if you've got a song idea and you're wanting to jamm it out, it's like having a live drummer in the room for as long as you need.

..or just ask me to lay some piano tracks down for you.  Don't even bother to write in the changes.