Okay just bought it last week. I like it a lot. Let's get to the point about it.
Construction is solid as a rock, it's 1 1/2 times the length of my QWERTY keyboard, so it has a reasonable footprint on my desktop. The keys, they feel heavy, it definitely doesn't have a cheapo feel to it. The knob and sliders, unfortunately, are made of plastic so I bet it would be pretty easy to lose those things in a good fall. The pads are stiff, just like the dozens of reviews I've read on them. They aren't unusable, just stiffer than they need to be.
Ease of use, that's where this thing suffers the most. It isn't impossible to figure out, but that's more of a credit to the FL Studio 9 "link to controller" option then the MPK's ease of use. I have searched and searched for support for this thing online, even Akai's website AND Image-line, so far, nada. For user's who have a strong background in MIDI mapping, the documentation that comes with this gem probably is really useful, for the rest, expect a pretty sharp learning curve if you want to tap into the full potential of this beast. For instance, mapping the pads to FPC, whew, not so simple as mapping the sliders to the Fruity Mixer. It can be done, however, and hey, everything can't be plug n play, right?
Finally, compatability with FL Studio? Well, so far, thanks to creating a template by linking all my controls in an empty session, then saving it, It pretty much is doing about 75% of what I want it to do. When I plugged it into my Win 7 box, FL Studio recognized it in the options, without using the drivers supplied with the CD. So, depending on how deep you want to get into this machine, it pretty much has the capability to control FL Studio to the extent of rarely ever even touch your mouse. Cool! But, don't expect that it will do that right out of the box, at least not with Windows 7 and FL Studio 9.
In conclusion? Great tool, just need a smarter user than what I got access to in the studio! (Umm...that's me, of course!) I never used an MPC before so maybe it's more intuitive if you're coming from that experience. Anyway, so far, one week into it, I have no (major) regrets, and I'd bet you wouldn't either. Holla!