Well, I'm not Apple, but just another user. In reality, since I don't have an iPhone or iPad, I really have little use for iCloud. Just thought I'd keep up to date for later. Anytime major changes take place, you will definitely encounter problems. I suspect in the future, things will be much better and no one will be complaining.
I only thing I can see that bad is that MMe had real cloud storage (iDisk) as oppose to what iCloud offers. The biggest difference between MMe and iCloud from what I can see is a different server and different way to log into it to activate.
I've heard there was going to be a SL update to 10.6.9 to accomodate iCloud. I don't know if it will happen, but we'll see. I believe MMe will be active until July according to what I've read.
If the Mail you can't send or receive from is on your computer and is MMe, then it's because when you moved your MMe account on the iPhone to iCloud, it merged the address into the iCloud servers it changed the way it would have to be setup on the Mac in SL.
If that's the case, change your email settings on your mac to these:
http://support.apple.com/kb/HT4864