I couldn't wait and decided on the JVC KD-SH99. I ordered it for about $320 from onlinecarstereo.com (good prices, reliable ordering/delivery, free shipping on orders > $99).
No offense to any of the Kenwood people (I installed a KW [non mp3] unit in wife's car), but I went with the JVC because the Kenwood MP3 unit seemed flimsy. When I pushed the buttons, the whole faceplate bowed and flexed. For as much as I dink with my radio, I figured this would annoy me after a while. Of course there are a number of other reasons too (4V outs which seems good, sub outs, ability to turn off internal amp, supposedly faster MP3 access, a real volume knob, included remote control, etc). I spent time on highwaymp3.com and read a lot of the message board entries for the Kenwood and the JVC, and I felt better about the JVC.
I know I complained earlier about the aluminum finish of the JVC, but I wasn't going to let the finish stop me from getting what I think is a good unit. I did a test-fit tonight in the dash and I must say it looks pretty cool; a stark contrast against the mostly-black Explorer dash.
I used the Metra install kit from short-Circuit City. I'm mounting it upside-down so the CD player is on top and the (useless) slot is on the bottom. I supposed you could put some small switches in the slot, but you'd have to fashion some sort of faceplate - probably not a simple drop-in.
I'm in process of a complete install this weekend (all power/signal/RCA wiring, plus MTX 4244 amp, also from onlinecarstereo.com), so I actually haven't even turned it on yet. :-( I will post my impressions and some install pics in a few days.