Here is something I don't understand with all the people complaining about not having a 32 bit version. You really have had to make an effort to buy a PC >NOT< capable of running a 64 bit Windows OS in the last 3+ years.
So your desktop hardware 64 bit capabilty as administrators should not be an issue unless you are using a 5+ year old machine. In which case I have to question why you are trying to upgrade your email system every 3 years when you can't seem to upgrade your management machines as frequently.
Remember - most of the cool new end user features require Office 2010 (like mailtips), and I really hope you all aren't planning to run that on Windows XP (which came out in 2002 - 8 years prior to Office 2010).
So really - if you plan to be agressive in upgrading your email system every time Microsoft releases a new version of the product, then you should plan on upgrading you management machines as well. Doing one and not the other is just plain silly.
And no I am not saying you have to upgrade every desktop in the enterprise, but generally it's a good idea to keep your management machines in sync with your servers.
I would also like to HIGHLY recommend that enterprises start moving to dedicated management terminal servers. Not only does this give you centralized locations to apply service packs and rollups, but it allows admins to more easily separate their normal user accounts from their admin accounts, while also being able to give them the ability to disconnect and reconnect from anywhere they have connectivity (like VPN'ing in from home).
Trying to install Exchange management tools accross 100 management machines in an enterprise, and keep them all up to date (this is often key with service packs and roll ups), is really last decade's way of doing administration.
Really - the writing was on the wall when they 64 bit production only version of Exchange 2007 was announced years ago, and it's only logical that the product group drop support for the 32 bit version altogether.
You really don't have an excuse not to keep your management machines in sync with the production version of the email product you are rolling out to your end users.