My "I don't need it but I want it" technology purchase this Christmas was a Roku.
I spent several hours early on the Christmas break trying to build a XBMC raspberry pi media center to act as an office jukebox. This worked ok, but I learned two things. One, it doesn't like to run "headless" (ie, without an active screen) and two, you really need a powered USB hub if you're going to plug in any non-trivial (ie, not a keyboard) USB devices, such as a wifi dongle or a USB hard drive.
Anyways, as fun as that was, I wanted something more polished, and picked up the Roku 3 at Radio Shack. In addition to playing my music collection, it can also do Pandora, Netflix, and a few thousand other things.
So, it's kind of overkill for what I wanted - just an easy way to play my music with a simple remote control - it's a fun toy, and also a great way to watch Netflix in the evening.
It's also interesting to compare this with the Google Chromecast that I picked up at LinuxCon a few months ago. While the Chromecast is a cool device, it's *way* behind Roku in terms of content and apps, and it's going to take a lot of catching up before I'd consider using it in place of the Roku. I'm sure that they'll get more content, but they may have already lost the race.