Three issues: Cost, size, and speed.
And their long-term reliability is still in question.
Plenty of 60 GB and 80 GB SSD drives available for under $100 now... but above that, you can easily pay $235 to $285 for one that is fast and rugged.
There are price drops nearly every week... while 12 different manufacturers know this is the cash cow. They are all rushing to beat their competition.
After Christmas, there will be 350 GB to 500 GB drives at a reasonable price... Then if they work well, two years from now, you probably will not find many regular hard drives still on the market.
We just received our first SSD drives on the first of July... and so far they are impressive... Quiet, relatively fast, but not nearly as fast as a Good Western Digital, Samsung, Seagate, Fujitsu, or Seagate hard drive... But they are now up to $350 for 250 GB.
Now if we only knew something about their long-term reliability... everybody speculates they will be good for five years... We will need to be convinced.
In the meantime there is nothing wrong with using a Western Digital, Seagate, Fujitsu, Toshiba, or Samsung drive that is 500 GB for $55... or a 750 GB for $80. Just avoid the unreliable TriGem, Hitachi, Maxtor, There are still plenty of problems with the 1TB 1.5TB, and 2 TB hard drives.. mostly with speed and early failures..