Though I believe most will fair better with windows media center and media center extenders, with the prime and "project connect" which is what they termed their dlna initiative you could use a bluray player or PS3 to access live tv... To see what some of the devices that work are, I suggest checking out their forum topic on project connect
. For me, all my content except locals is protected (just because it is encrypted does not necessarily mean it is protected... comcast and verizon usually mark all but premiums as copy freely so they are not protected) so I don't use much dlna in my house... I try it from time to time to make sure things are working.
The biggest problem you will have would be with protected content as currently their isn't a recording solution for protected content, in theory someone could get the proper licenses, etc. to make the pc a device that will support copy once content, but currently that is limited to WMC and not dlna. The advantage of doing it this way is for "live" tv viewing that you won't need a pc on. Protected content will require a device that supports dtcp-ip as well as mpeg2 (for most TV)... later this year they are supposed to release a version of the prime that will transcode the mpeg2 stream from the cable company into h.264 which is what most dtcp-ip compatible devices are compatible with... the only dtcp-ip compatible device that I am certain supports mpeg2 is the ps3. Keep in mind the interface for dlna is very crude and to get to an hd channel will probably require pressing the down arrow hundreds of times (one for each channel... some do offer page down capabilities that may mean you hit page down 35 times then navigate to the channel you want to view.
For unprotected content, recording isn't a problem and currently even my WMC recordings (as long as they are not protected) will play back in my old sony bluray player (WMP can act as a dlna server on the pc so nothing "extra" to install... there are other dlna servers (software for your pc) you can use that I think offer more features but I have had to tweak heavily to get it to work with certain devices less powerful ones, including those built into NAS devices also seem to connect well with most devices. I might check out jriver later this year as I heard it could function as a DMC which may make the interface better.
One thing to note is that the prime is a certified dlna device and as a result, must obey certain requirements to maintain that certification... one of these requirements is to drop a connection when a range tag is sent in the request... most of my google tv / android equipment that used to work, no longer does as they all now send these range requests but non-seekable content such as "live" tv can not respond to a range request (as it is "live")... most implementations of dlna simply discard the request but that is because most implementations are not certified.
As I began this post, for most, WMC and extenders will work better, but there is a lot to be learned and to play with doing things the "new" way.