Windows Home Server user there's a very good chance you've taken advantage of the drive pooling features of the OS. Need more storage? Pop in a new HDD, watch some lights blink for a bit, and then you're ready to get back to downloading... whatever it is you're downloading. Granted things didn't always work perfectly, but this tech, formally called Drive Extender, makes adding storage easy, makes it possible to replicate only the data that needs it, and is completely hardware independent. And now it's going away. Microsoft has confirmed that the next release of Windows Home Server, Vail (due in the first half of 2011), will not feature Drive Extender, indicating you'll need to simply buy bigger drives and manually handle data replication or rely on RAID to make this happen, solutions that are decidedly less intuitive for non-techie users. The reaction among WHS fans has been overwhelmingly negative, with 148 comments (and counting) on the announcement post, most telling MS where it can shove its RAID controller. Feel free to keep on venting here if you like.
Update: Malcom dropped this link into comments, where Windows guru Paul Thurrott indicates the issue is related to MS trying to position this to the small business sector -- that Drive Extender can't keep up with more professional loads.