I was just doing some research on this topic yesterday and today to try to find out more about the Pioneer F series. I strongly suggest you check out the avic411.com forums and there's a wealth of information there. If you're considering the F700BT check out this thread:
http://www.avic411.com/forum/viewtopic.php?t=15669. A lot of owners of the F700 pitch in and there's a good discussion about the F series vs the Kenwood 5120/8120.
A quick summary from what I've gathered so far. F700 has a LOT of show-stopping bugs (random freezing and/or crashing while looking up POIs, taking 3-5 mins to load up when the car is turned on, numerous bluetooth problems, etc). A lot of the owners of the F700 seem ready to return their units.
Advantages over other units: Voice activated ipod controls is supposed to be really cool. MSN Direct seems neat. Very nice looking interface and slick GPS maps.
Disadvantages over other units: Bugs bugs bugs (as mentioned above). Apparently in the F700/900 you'll sometimes have to press the interface twice before it registers (even tho it chimes the first time). And even without that bug, Kenwood's interface is still more responsive. Kenwood's GPS is Garwin so it's super accurate, much more so than the F series. Much more complicated bypass procedures (Kenwood you just ground the parking brake). The Kenwood 8120 absolutely BLOWS the F90BT out of the water feature wise, but the F700 is more comparable to the Kenwood 5120.
So unless you really really want the voice activated ipod stuff and MSN Direct, check out the Kenwood 5120/8120 (depending on your price range). I gotta say tho, the voice activated ipod stuff seems really cool....wish the 8120 came with it