We have an SQL 2005 database backend for our website, currently about 10GB in size. There are a lot more reads than writes, though I don\'t have the exact statistics.
I'd spend a little time making sure your database is efficiently indexed; monitor it for Full Table Scans, make sure the most frequent queries read as little data as possible; I'd take an efficiently designed database on a slow disk setup over a database with improper indexes on SSDs.