There is more than a few chinks -- MD5 is broke, its getting worse day by day.
look here (offsite:rub.de)
for an article that explains the current publicly announced state of things. I as this gets more eyes on it, it will get even worse. MD5 digests should be considered almost as insecure as mad XOR magic. =)
Update: just wanted to add that SHA-1 has some of the same weaknesses as MD5, but as of yet they have not been able to break it like MD5. If you are really worried you can goto something like Digest::SHA256
for a digest, but it may not be worth it yet.