I keep waiting for some of the media access interfaces for HTPCs to mature. I've found nothing that really worked in Linux and I've played with Media Portal for Windows, which shows promise, but still isn't there yet either.
Either way though, perfectly happy to use my old computer as an HTPC, it even has optical out so sound quality has been great. It eventually got cranky about the overclock though, I think the old Shuttle powersupply is starting to show its age. I can see the point of wanting to centralize everything on the HTPC, eliminate the separate components and just hook it up to the amplifier, but realistically I would never want to take it that direction. I'd still rather keep the separate components.