In terms of computing power, its overprized. But as a product that sits in your livingroom, problably not making any noise and runs under 10W, then I will actually call this a fair deal. May I add that its ridiculously small.
Use case: your laptop's hard drive fails so you yank it, shove in a new one, boot off the SD card, and use your Time Machine backup -- you've got one, right? You're one of the Saved, right? -- to restore onto the new drive. Total elapsed downtime from hard disk crash to up-and-running again: 1-2 hours plus however long it takes to source a replacement drive.
(The fact that you can get photos off your digital camera is an accidental bonus. Because, hey, your camera is an iPhone in Apple-land ...)
Previous, not last (last is mid 2010, SD slot appeared on mid 2009 machines)