I think it depends on whether or not you can find something to take the place of Access, which doesn't exist on the Mac. There are some alternatives like Bento and Filemaker, as well as some good visualization packages, so probably yeah you can make it just fine. Excel and Word are available for Mac, as is PowerPoint.

I would check and see if iWork 09 will do what you need it to in terms of spreadsheet and document editing - I think Pages in particular turns out better looking documents (especially layout type stuff vs. manuals) with less effort than Word. Numbers is not high powered, though, and it may not be able to replace Excel. Keynote on the other hand - you are going to LOVE it and never look back at PowerPoint.

Mail will be no problem, the built-in mail that comes with Snow Leopard works great with Exchange (or you can use Entourage from MS but I like Mac mail better).

The other potential gotcha is Quicken, but their long-awaited Mac version is due out right after the first of the year. I use it on my Mac right now in a virtual Windows session with no problems.

So...you'll definitely save time and hassle by switching, and have a more aesthetic computing experience to boot. That's not to mention great-looking presentations coming out of iWork. But be prepared for a dip in productivity for a week or two while you become accustomed to all the new stuff.