I have it and I really like it. Here are the specifics of it. First, what you heard is correct - you can't feed DVR to DVR yet (although I understand that's coming). You need to have an STB on one of your other TVs to get the recordings (either the SD STB - the QIP2500, or the HD STB - the QIP7100). If you want to access HD recordings from your DVR, the other STB has to be the HD version. You can only access SD recordings from the SD STB.
In terms of how many - you can feed out to up to 7 STBs. You can even feed out more than one concurrently. You can access 2 SD recordings at the same time (you can even access the same recording from two TVs at the same time, independent of one another), and watch a third, either SD or HD, directly off the DVR. If you're accessing HD remotely, you can only access 1 recording from the remote STB at a time, plus a second off the DVR directly.
I have the HM DVR, with one SD STB on another TV. I don't have any connectivity issues - those with HD STBs have indicated that sometimes they lose connectivity from the STB to the DVR. I've only seen that issue once, and apparently there's a fix in the works for the issue to the HD boxes. From my perspective, the DVR works remarkably well. Yeah, the harddrive is small (they really need a bigger one), but the PQ on the remote TV is excellent.
There are a couple nits I hvae:
1) You can't manage recordings on the remote STBs. For example, from my SD STB, I can access recordings, but I can't set up new recordings, or delete one that I've watched. I can only do that from the DVR itself (or from the internet - you can do remote DVR access over the web).
2) The response on the remote STBs is laggy. If I hit pause, e.g., it takes a second or two for the command to register. The reason is because of how the feeds work. They go from DVR -> router -> STB. Commands to the DVR have to go back via the same path. Access from the DVR itself is really fast, but from the remote STBs it's laggy.
There are also a couple other features that are specific just to the HM DVR. You can access digital pictures and music from your PCs, and they just added video as well - both home video, and some internet video sources (YouTube, e.g.). Which leads to the next nit:
3) I can only access my digital media from the DVR itself. I can't access them from the other STBs.