There are lots of factors pushing the prices down on the 08s:
. end of the model year
. free premium package thrown in
. what looks to be a glut of inventory in the channel
. SUVs out of favor, being attacked by the anti-car crowd, esp the v8

I was able to negotiate a price of more than $1k under the 'invoice' price, but because of the premium package trunk money, the dealer walked away with some money in his pocket. At the same time, I believe BMW has a holdback scheme of approx 3% with minimum required sales volume, so the dealer is also incented to move product.

The x5 I ended up buying didn't cost the dealership anything: didn't come out of their allocation (they ended up pulling it from another dealer), it wasn't sitting on their lot costing interest, etc, so I was able to do a quick low overhead deal.

You completely lose this leverage with an 09 order. The unfilled order isn't costing them anything, and the dealer will think that someone will walk in and pay a much higher margin than the 08 close-out prices... Cars on the ground and in their books cost them money. Unfilled orders do not.

As far as I know, there are limited changes coming to the 3.0 and 4.8 models, and those are detailed in the sticky ordering guides. Some packages have gone up, plus they include other things now. Full leather dash is available. And there is a price increase. New iDrive coming mid-model year, and 2 new models coming mid-year too: diesel, and rumor is that a 4.4l v8tt will be introduced as the 'iS' version.

All that said, if you want one now, want a 3.0 or 4.8 with typical options, and you plan on keeping it for a few years so you don't car about the instant depreciation, I would go for the 08 and save significant $$$.