Well, I won't be buying Diamond or Pearl when its released because quite frankly, I don't want to buy a DS.

However, IF I did own a DS, I think I would end up buying Diamond rather than Pearl.

In terms of version-exclusive Pokemon, Diamond gets Scyther/Scizor, the Tyranitar line, the Aggron line, and the new Headbutting Fossil Pokemon, whom I think is a WHOLE lot better than its counterpart.

And the other thing that also caused me to pick Diamond over Pearl is of course the Legendaries. I like Diaruga's typing a whole lot more than Palkia's, cause a Steel/Dragon mix doesn't really have any weaknesses to anything (not even Dragon itself since I believe Dragon is weak against Steel, thus making it normal damage to a Steel/Dragon type).

But other than those aforementioned features, I don't believe there is much else that is so significantly different between both versions