I had just performed an exchange 2003 to exchange 2010 migration. First off, this went flawless! I was so happy with the outcome. As many of you know, Exchange 2010 requires 64 bit OS. THEREFORE, I started the projected by creating a new 64-bit Windows 2008 enterprise server and a new windows 2008 64 bit enterprise domain controller in an existing 2003 active directory environment. First, let me say that you have to run adprep off the 2008 cd on your DC that holds your fsmo roles. I installed exchange 2010 and brought up a new BES 5.0.2 server as I thought this would be an excellent time to refresh corporate blackberry users. I love this version of exchange! I was running co-existence mode until the migration was complete and then I uninstalled exchange 2003 from my environment and retired that old clunky exchange server. Let me say that despite the noise about making your client access and mailbox role a VM. I had no issue doing this, as I am a huge VMware and virtualization fan. I have had no issue with my cas, hub, and mailbox roles all in one VM with zero performance issues. One thing I do not like is that by design store.exe is now a memory hog! However, there are parameters that you can use in adsiedit.msc where you can limit the memory usage of store.exe that work great! All in all the only complaint I got was from the helpdesk, as they cannot install Exchange management tools on their desktops because they run 32 bit OS. I told them to upgrade their desktop OS to 64 bit so they can run the tools. I know they make some third party management tools that allow your helpdesk to still perform common exchange tasks but I am NOT a big third party fan. If anyone has any questions about more details about my migration from exchange 2003 to 2010 I will be more than happy to answer them. In addition, when you plan your exchange 2010 rollout one big thing to remember here is give yourself plenty of space for the info store lun as exchange 2010 does NOT like to have less than 2 gb free space of the store lun or luns. If it goes below 2 GB mail will stop flowing and will not flow again until you free up some space.
Frank Bicocchi