The first human genome cost $3 billion to sequence back in 2003. By 2009, the cost to sequence someone's genome had dropped to more like $50,000. Next year, the target is a mere $1,000, and it'll only take two hours to completely identify all six billion of the base pairs in your DNA to tell you what you're likely to die from first.
The reason why sequencing your own genome might be something you want to do is that you can use the information contained in your DNA to figure out what hereditary traits and diseases you might be susceptible to, and if necessary, which drugs would be safest and most effective to use. Right now, it's possible to sequence little bits (important bits) of your genome for a couple hundred bucks to check for susceptibility to some specific diseases, but looking at the whole thing provides a much more detailed overall picture.
At 6 billion base pairs, the human genome is much smaller than some species of plants, fish, and amoebas. Go figure. Anyway, in order to properly sequence an entire genome, you basically have to go over it ten times or so, which means sixty billion base pair IDs. We're transitioning to being able to do all of this stuff on computer chips, which is why the process is getting so efficient so quickly. A company called Ion Torrent is already producing desktop genome sequencers (complete with touchscreens and iPhone docks) that can complete gene sequences of bacteria in just a few hours, and by next year, they're hoping to be able to upgrade to humans, too.