First of all there is a hell of a lot that is great with Exchange 2007 when you include SP1. My hats off to you for making a great product.
If you're looking for crtiticism, then I'll keep it to only that. Powershell is awesome and I didn't understand its strength until attending the Exchange Customer IT Fellowship program here in Redmond last week and this. But (there is always one isn't there?)... your typical every day Small-Mid sized business Windows admin is not going to have time to learn a lot of these cmdlets not available through the GUI.
I think the GUI should retain at least the same command set the E2K3 tools had and then if you want to split it off from there so be it.
Personally I work in a highly decentralized environment with centralized Exchange services. We have hundreds of site-level OU admins across our org who I can tell right now will never be able to learn powershell. They either lack the skill or the will to learn something new. I can hear it now "then why were they hired?"... well, why were most people in gov't hired? They probably know someone or have been there for years and are union boys and gals. These are folks who simplly need to be able to create mailboxes, check the current size of their users' mailboxes, add secondary SMTP addresses, provision users through ADUC, and other low level (or high I guess, depends on your definition) functions.
A lot of these tasks are now only doable through Powershell or the separate Exchange Management Console. I'm going to have to write scripts for them to run or spend a lot of time training them. Giving them scripts isn't too bad, but I'm afraid there is far more possibility for them to play around and instead of mucking up a couple user mailboxes, they'll affect hundreds instead.
AD and Exchange were joined so nicely before and to me it is a shame to see them becoming separate again. Please do not assume all organizations have seperate AD and Exchange departments. Give us the ability to keep it the way it was if we so choose it.
If it is of any kind of help, our profile is a 34k+ mailbox org growing on pace to be over 40k very soon. We have a small centralized Exchang/AD team (8 people including managers) and then a bajillion site level admins out in the field doing front-line user and file/print/db support and whatever else their agencies need.