How do I transition from a MobileMe account to an existing iCloud account? I'm starting to get more messages about MobileMe ending, but despite all the info people have been posting online, I'm still confused as to how to deal with my own situation.  

I currently keep all my contacts, calendar, and probably a few other things on MobileMe, and have my devices tied to that account's Find My iDevice function.  

However, I use a different email address for my Apple account (app purchases, Game Center, etc.). I believe I've already created an iCloud account using this email, though I'm not sure if I have anything on it yet.  It seems that Apple really only wants you to have one sign-on for iCloud, the app store, etc., since you can store your purchases there.

It sounds like I can't really merge the MobileMe data into my existing Apple/iCloud account.

It sounds like some me functionality is going away (ie, not replicated by iCloud functionality).

What do I need to do to keep my calendar and contacts synced across all my computers and devices, and how do I move them from my existing MobileMe account to my existing iCloud account?

Can I still keep my @me.com email address?  

Does iCloud have an email account/address that comes with it?

It seems like I should be able to wrap my head around this myself, but it's still unclear.
Here is a fantastic article on moving to iCloud. http://support.apple.com/kb/HT4918

And, yes, you can keep your current @me.com address. Instead of being associated with MobileMe, @me.com email addresses are now iCloud (and MobileMe user will be migrated over), so the email address that comes with iCloud is @me.com. Again, I believe you are able to keep your current @me.com address.

Unfortunately, merging wouldn't be possible.