...approximately 1,600 passwords appear unsalted. Cracking unsalted MD5 hashes is a pretty elementary task with rainbow table or brute force attacks....
I wouldn't call that cracking. With 1,600 passwords, it would take a computer less then a second (my guess) even with a large rainbow. I could be wrong.
Any crackers want to enlighten us on this?
It all depends on how strong your password is...
Some numbers: Have a look
http://project-rainbowcrack.com/table.htm at the bottom of the page where it says "md5_ascii-32-95#1-8". A table with with all passwords with a length of 1-8 characters in the complete ascii space is around 600GB. The longer your password is, the bigger the table needs to be... and this also needs to be generated.
That's also why you need to hash your passwords if you store them. The rainbow table needs to be generated with the hash that's used on the site...