Mihai -- Why are you saying "it's impossible to integrate exchange with the current SQL Server"? Statements like that drive me nuts when they're not backed up with any facts.
Personally, from an enterprise perspective, I'm disappointed that MS is again passing on SQL integration. In larger environments, integrating with SQL would be substantially cheaper from a number of perspectives. For one, we'd have a TRUE "single instance storage" -- today, because of practical limits to how many mailboxes you can have in a mailbox store, we have a single message going to several stores on several Exchange servers. That also means that other enterprise concerns (like legal discovery and litigation holds) will be a substantially easier topic to swallow when there is just a single database.
For the bigger folks that already have an established SQL infrastructure and talented skillset, SQL is definitely the better way to go. Personally, I'm disappointed that this is getting passed over yet again. I've been waiting for this for years now.