I've got my reservations about the lack of an optical drive, but they're minor. In general, this looks like a really great deal for a business, probably one of medium size.
I'm torn on the pricing. On the one hand, $999 for the unlimited server license and some very capable hardware is a screaming good deal. But it's a bit stiff for me to have one at home at that price. (A ten user version would help, but I'd still find it limiting since I have...ah..."a few" systems here.)
Mac OS X 10.5 Server started out for me as a rocky road, which was a surprise given the reliability of 10.4 and 10.3 versions. But eventually the software updates did iron out a tremendous number of the problems and got 10.5 Server to the point where it was usable for the work I had in mind. (Strangely enough, the Mac Mini had a little bit of a fit today.) I've been using a Mac mini (Intel 945, 4GB RAM installed and usable, 320GB boot drive) as a workgroup server with Mac OS X Server. It provides Windows domain services to approximately twelve Windows XP clients and DNS services to a mixed network of about 30 systems. It works very well for these tasks.
Those who point out that Windows Server can do some things that Mac OS X server cannot (or does not do so well at) have a point right up until you consider the licensing model. Having set up a few Windows servers, I can say that the Microsoft licensing model comes across as needlessly confusing and complex. I still administer a Windows Server 2003 Terminal Server that I honestly hope is properly licensed. It *should* be.
Mac OS X server's attitude about this is much better--just pay one price and you can have as many users as the computer will stand. I would love to see Microsoft do the same.
Windows Home Server is an interesting product as well. I tried the 180-day demonstration (but only for 30 days, as they never sent me a demonstration product key) and it felt like a quickly slapped together software product. The installer was part Vista, part Windows Server and lots of hotfixes rolled up into one. And while you do get a desktop and the ability to log in to the server, Microsoft
strongly suggests that you not do so for any reason, as the possibility of breaking something is very real. Yes, that's what I want from a server.

I would like to see Apple do a cheaper version for home and small business use...maybe with a little less onboard disk storage, unlimited users and a price around $700 or so. Then I would find it very interesting.