It can vary GREATLY. Just checking out a few drives on Newegg, I see one:
Sequential Access - Read: 220 MB/s
Sequential Access - Write: 135 MB/s
Sequential Access - Read: up to 25MB/s
Sequential Access - Write: up to 8MB/s
A lot of SSD drives are pretty comparable to regular (though they vary much more)... They're big advantage is non-sequential reading/writing, because it doesn't have to spin to a certain spot on the disk, it can read and write anywhere at any time.
This conventional harddrive:
Sustained data transfer rate 138Mb/s (11.5 MB/s)
Average latency 4.16ms
Random read seek time 8.5ms
Random write seek time 9.5ms
So some of the faster SSD drives are faster than traditional drives, and some are slower. As they get better at making them you'll see them going faster and faster because they aren't limited by the same constrains of spinning disks.
These stats aren't always all that meaningful though. The best thing is to probably check out benchmark tests for more real world results like here:
There are plenty of these out there:
But you'll find the more recent ones are going to show SSDs in better light as they have been improving recently.