I've got the little low power Intel D945GCLF2 based system at home running Lion Server now.
I use this system primarily to backup my projects at work to an offsite location. It monitors the Windows server at work and syncronizes a copy of it's data files locally for an offsite backup using Superflexible Syncronizer. It also contains all of the family photos, music, movies and raw video which it serves up using Twonkymedia's DNLA server for the home theater system and Zumocast for access to streaming music on our Droid 3 phones.
It took a couple of tries to get it running Lion, but it does it nicely with a modified kernel for the Atom processor. The server installation is interesting. Lion basically already has all of the services necessary to be a server, but the server software adds the ability to configure it properly for use as a server.
I've only just scratched the surface on Lion server so I'm not about to replace my Windows server at work, but who knows? If I could push email, calendar and addresses to my phone I might just consider it. (And yes, there are reasons why I don't have an iPhone that would allow for this…)
