Now, the problem is that what is essentially a piece of molded plastic with a couple of buttons is very expensive. It's $250 from Adorama and B&H [plus $40 shipping to Australia], and grey import it's about $270 (ex GST). I dunno what it would be from a bricks & mortar camera store, but probably around $400 would be my guess! For that kind of money you can buy a lot of lens or even a good 2nd hand entry level DSLR body. What a rip!
So - it's been on my wish list for a while, and wasn't looking like it was going to be marked off... But, about a week ago a Phottix BP-D300 appeared in one of my ebay alerts. The Phottix BP-D300 is essentially an exact clone of the real deal Nikon MB-D10, but at about a third of the price. Let's just say I didn't have to think very hard about making the purchase. I've also got a Phottix Timer Remote (clone of the Nikon MC-36) which has been excellent.
The BP-D300 arrived on Friday and I attached it to the D300. Initial impressions are that the plastic is not quite as good as the Nikon, but certainly not too bad. The BP-D300 comes with two battery trays, one for the extra EN-EL3e, and one that holds the 8 x AA's. It certainly makes the camera a lot bigger and heavier, as well as making it look more professional (and expensive). All the buttons work as advertised and the camera detects it as an MB-D10. There are a few negatives though:
1. The shutter button doesn't feel anywhere near as good as the one on the camera body. The half press feels quite weird - it's like pressing a button, not just getting to the first stage of a press. And when pressed fully you get a loud click.
2. When loading the AA battery tray, the clip doesn't lock easily - you have to push the tray in harder than you'd expect to.
3. The plastic... as mentioned above.
The other minor niggle, is that you can wiggle the battery grip very sightly independently of the body. I would guess that the Nikon MB-D10 would be similar because of how it's designed, but I'll check this next time I use the genuine one.
The BP-D300 also comes with a cigarette lighter adapter which the packaging claims to recharge the EN-EL3e. I haven't tested this out and I don't think I ever will as I prefer and trust the charger that came with the camera.

Summary: I've got no regrets - it's a great addition to the D300. Buy one now and save heaps of money over the MB-D10 to get something almost as good.