Better than nothing
This is just for when you ship physical media to bulk import into S3. It's optional to protect the data in transit. If some random postman grabs your HDD then I think it's unlikely they'll be able to decrypt your TrueCrypt volume. Surely still a much better option than no encryption at all.
Out of genuine interest, do MS or Google's clouds offer import of encrypted data when you ship bulk data?
Even better would be to encrypt it yourself then wrap it in Truecrypt, at least that would delay anyone wanting to have a nose at your private data before it's dumped onto, a, gasp, public, cloud. Oh.
I'd also much prefer to use something that's open source (apart from the Win binaries) and auditable rather than something who's sourcecode will probably never see the light of day.
You've got to worry who's doing the audit though. I mean, who's really doing the audit?