They excel in random reads and writes when compared to hard drives, because the data is not on a spinning platter. Access times are extremely low for the same reason. If we are talking sequential reads often time a high performance hard drive can approach "affordable" ssds, but it really isn't that significant because most reads and writes performed by most programs and your operating system are non-sequential.
Downside is that SSDs have a limited number of writes before the NAND is unusable. There is no way a home user would ever reach this number unless they have it under constant heavy usage for years in a row.
You can't "upgrade" the storage without buying a new drive. The memory chips are soldered to the drive, and often times the ssd controller is set to over-provision space to improve the drive's longevity.
Also, unless you are using an OS that supports TRIM (
http://en.wikipedia.org/wiki/TRIM#Operating_system_and_SSD_support) then I would not bother.
My recommendo: Buy a Crucial M4 256gb. Install your OS and programs on that drive. Put all your files and crap on a secondary drive. Though you are probably using a laptop so that last part would be a little problematic...