A friend sent me this link: Microsoft adds Slingbox-like capability to its Media Center PCs. I spent the better part of this evening playing with it and I have to say: this is hot. I can log into my media center box and stream any recorded TV program or music in real time. The content is transcoded into a lower bitrate/resolution on the fly. I can almost stream recorded TV over T-Mobile's EDGE network (but not quite...too much stuttering while buffering). It's not as nice as watching the actual program on my actual TV, but if I'm, say, staffed out of town and I want to catch a show I recorded, it will get the job done.
Edit: Here's a photo of M*A*S*H streaming to my phone over Wifi. 15 frames/sec, 160x120, 100kbps.