Thanks everyone for the notes - I'm not going anywhere. As evidenced by the responses, this is one great bunch of people that stick together and have fun doing so. It would be tough to go elsewhere, though I am lurking on e46 boards to see what may be waiting to bite me in the arse.
Specific responses:
Warren - I have driven cars that have that hovering throttle bit, this one doesn't. Not sure if it's a function of the reprogrammed ecu on the ZHP motor or if it's a general change in the M54 motor. The M54's came available with the change to the 325/330 (from the M52TU in the 323/328), and that's when the throttle response profile may have changed?
Drew's comparo is spot-on (and luckily I'm confident enough to handle the loss of 10" in length). I havent' looked at specific numbers, but I swear there is more legroom in the back seat than in my 535.
Dick - the wide grill is BUTT UGLY!

Luckily, the M front aerodynamics provide MASSIVE brake cooling to the huge front brakes Drew noted. There shouldn't be any problems with overheating them!
Jr - I'm already trying to steer people on the e46 board over to BMA - some people there are under the mistaken assumption that OEM parts must be bought at the dealer. We'll fix that soon enough!
Peter, Jeff, and everyone - thanks for the help, laughs and support over the years. As I noted - I'm not going anywhere - too many good people here.
Driving impressions? Thought you'd never ask. It's not like I can open the thing up yet, but it pulls nicely. Perhaps less relative low-end than an M30, though it's made up with the short rear end. I haven't been above 4500rpm but once, and then by mistake, but the sucker pulls hard above 2500 or 2700 rpm, like one would expect a dual cam motor to start pulling. It's rated for 30mpg on the highway, and the gauge was showing better than that in 6th gear, that's nice. So I can't really comment on speed and power yet, but what I felt is gorgeous. More on that soon, I hope to hit an autocross or track day later this summer when things are loosened up.
It TURNS, NOW. Point the wheel, and you are there. There is no such thing as body lean. There is no lag in the car responding to the steering input. The steering gear is actually a faster ratio than even what BMW puts in the M3, so the car is VERY responsive to steering inputs, and the 18" rubber puts those changes to pavement RIGHT NOW.
The brakes STOP like MAD. Not much else to say there. They feel great, I was going easy in bad rain last night, and never triggered the ABS. But reading about all of the DSC and CBC and other acronym functions - the thing should brake really nicely. The adaptive brake lights out back are pretty neat too. Lighting in general is great. I got a car with Bi-Xenon, since that's what was available without waiting for a factory order. The new xenons are adaptive to load leveling, turn a bit as you steer in turns, and the xenons now do both the low beams and the high beams. TONS of light out there, which is good with all the damn deer where I live.
The best single evolutionary growth in convenience has to be rain sensing wipers. Set the sucker on high-sensitive, push the stalk to interval, and I never had to touch them again. Last night I went from light mist (slow interval) to massive downpours (fast wipers) and had everything in between. The car just adapted.
I really like the interior. For years I lurked around here looking (drooling is a better description) at the shots of Euro M5's with the cloth sport seats that were not available in the US market. Well, these are an advance, in that the bolsters are all nice, grippy alcantara. They feel great, grab your ass firmly, and should wear nicely. The steering wheel is also a really FAT rim, covered in alcantara. I won't be able to eat any french fries in the car, but so what - the wheel looks great and feels incredible.
There are cupholders, two nice ones! That's a nice evolution.
The short shifter is not as short as it could be, not as short as the Stygar-ized MZ3 shift lever I had in the 535. But it's better than other factory shifters, and it will do for now. The surround is alcantara to match the seats and wheel and looks pretty nice.
The upgraded exhaust is also nice - it's got a great grumble without being overbearing. Definitely louder than my mother's 330Ci, but definitely not a Billy Boat. And the brushed stainless tips on the muffler are not caps, but actually the steel of the muffler, brushed down and sealed. Dead sexy.
As I noted, the weather last night was SUCK. Once in the garage the lighting was worse, so there are no pictures yet. Maybe some tonight, definitely this weekend. The details like the front and rear airdams, the completely covered and smooth aerodynamics underneath, the exhaust tips, the steering wheel - they all deserve some attention. I'll give it as soon as I can get some good pictures.
--Micah O'C