Fenixp: Well as long as you don't care about the inherently terrible effects of digital preorders, sure, the 10% discount is worth it. Nonetheless, if you want a discount, you can get much better deals than that. If you want to support a company, you can give them 10% extra money on release. There's just ... Nothing worthwhile about preorders. I suppose there's use if you don't want to manage your money and just want them spent straight away, but that's not really a particularily good reason to support a culture which leads towards giving exclusive content to players who choose to preorder and is specifically designed to lead towards reckless purchase decisions and to abuse consumers who have psychological issues with flash purchasing. (is it what it's called? I don't think that's what its called.)
I guess I don't care about the inherently terrible effects of digital preorders, no. Or rather, I don't consider them so terrible. As in, if idiots want to keep throwing money at Ubisoft for doing terrible games, that's certainly a pity, but it's their money. I wish they spent that money buying Deus Ex copies, but I can't have the world go my way. We'll keep having terrible games, which I will not be buying; and we'll keep having good games, which I will buy.
As for the exclusive content... I honestly don't give a crap. It's fluff anyway, and it will typically later on be available on the GOTY edition anyway that I might be buying.