You can benchmark the speed of your SSD or hard disk using a few simple Terminal commands. To test write speed:
In the output, you should look for something that looks like "bytes transferred in 16.546732 secs (519131791 bytes/sec)." Copy and paste the bytes/sec speed into Google to convert to MB/s (e.g. Google search for "519131791 bytes/s in megabytes/s").
time dd if=/dev/zero bs=1024k of=tstfile count=1024
[kirkmc adds: While we're on the subject, here's an easy way to test data throughput from one disk to another. Open Activity Monitor (in /Applications/Utilities), click on the Disk Activity tab at the bottom of the window, then look at the Data read/sec and Data written/sec numbers. Copy a large file from one disk to another to see how fast it can go. FWIW, my new Thunderbolt drive has throughput of about 100 MB/sec.
dd if=tstfile bs=1024k of=/dev/null count=1024
Mac OS X Hints