The HTPC is dead.
There are a few things taking it's place.
1. For tweakers, the new thing is the media extender. Nobody wants to build a HTPC for each TV. It doesn't make sense. And the MCE extenders are pretty limited in format support. So, the industry is moving on. The popcorn hour is great if I just want to play downloaded content on your TV or ripped movies. But, the real star of the show is the SageTV HD200. As an extender it is great at playing downloaded content, even BD rips, but also adds the capability to connect to a central headless server (the best run windows home server), and you can even take a HD200 with you as a placeshifter, accessing all your content on your server from the road. On the server, you can have as many tuners as you want to record TV, and with the new Hauppauge HD-PVR you can record component HD signals up to 1080i from your cable box straight to h.264 in real time via a built in hardware encoder. No CPU heavy lifting required. String two or three of those tuners together on a WHS computer, buy a $180 extender at each TV (7W of power each) and you've got a powerhouse of a system. You can rip your disks to the server (DVD or BD), rip your music, record your TV, store your pictures, host your website, backup your computers in the house, and bring an extender with you on the road to access your content. It is actually a really really really powerful system but it does require a bit of tweaking. Nothing a person who is confident with computers can't handle, but the average joe isn't that confident. If you ever consider taking your computer to Geek Squad, this isn't for you. Still the only hassle is setting up the server to record your shows and store your content. The big hassle with HTPCs used to be getting your content to play, fiddling with audio and video codecs, getting the right video card, making sure your CPU could handle BDs. Now with extenders, it just works once you plug in and configure the resolution and audio output. It has made it MUCH easier.
With PlayOn you can get access to Hulu and some other stuff but that requires a bit of tweaking.
They are also launching a version of the server that runs a version of linux off of a USB stick for non tweakers. You buy or build a small computer with the types of HD tuners you want like the HD-PVR, stick this stick in, boot, and it configures the harddrives for recording and runs the server from the stick. Pretty cool actually. It can even do RAID on multiple harddrives for backup and pooling of multiple drives. As much storage as you want...
2. The other big news in HTPCs is Boxee. An offshoot of the venerable Xbox media center that used to be so popular on modded 1st gen Xboxs, this software is aimed at the social aspects of entertainment. It is a media player that can play your downloaded content or ripped disks, but it will also connect to online sources like Hulu. I'm not an expert in it but I've played with it a little bit installed on my AppleTV. Boxee will run on Linux, Mac, or a PC. It will also run on an AppleTV but the appleTV is too slow for much of the content Boxee can play. If you really want to hook your notebook to your PC, then installing Boxee to access your content is probably the way to go rather than Microsoft Media Center or Front Row.
3. Integration into TVs and BD players is also big. Panasonic has Viera link where you can access Netflix and Amazon video rentals as well as YouTUbe and some others, and the BD players are also supporting the same kind of networked content access, but no standard has yet emerged that will make it easy for each manufacturer to get content. It is done with one on one dealing with each hardware making and software maker. This is terribly inefficient and so I don't think it will last too long. We must find a few 3rd parties who write the software to integrate these services and then the TV makers just need to support that universal software. 2 or 3 different systems are fine and lead to competition and innovation, each TV and BD manufacturer on their own is not. Boxee wants their software to run on these systems so it may be coming, but I don't see it yet.