Removing the motherboard entirely isn't too difficult - just make sure that everything is disconnected (IR sensor, power supply line; I got away without disconnecting the wireless antenna, preferring to carefully maneuver it out of the case with the motherboard). Just be careful for a rubber covering around the power supply. Mine popped out when I removed the motherboard; it seems easy enough to replace, but when I closed up the motherboard for the first time, the rubber contorted and covered the power port. I had to remove the motherboard again in order to reposition the rubber.

Best of luck to you if your hard drive is in the "lower" position. Having done it once I can do it again, but I never want to. I've opened many Macbook Pros, but this Mac Mini is far worse... (comment 2/2)

This guide left out some very difficult steps for me. The Mini has two hard drive slots, and this guide assumes that the drive is in the "upper" slot (closest to the antenna plate). On my machine (refurbished Mac Mini late 2012 purchased October 2013) the hard drive was in the "lower" slot, and was firmly screwed in to a holding post. In order to reach the screws the motherboard needs to be completely taken out of the machine, and you'll need a really long-necked or a really tiny Torx screwdriver. The drive is still held by two rubber stoppers; I couldn't find a way to remove the plastic mounting bracket, and the screws required a surprising amount of force and jiggling to free the drive. I couldn't find a way to re-secure those screws into the bracket holes, and just forced the drive into place. Unless you want to forego or modify the black cover for the drive, you need to replace the drive in the "lower slot" because the cover isn't cut to reveal the drive's upper screw holes. (comment 1 of 2)