Looks like it's more expensive than S3 at this moment. USD 0.17/GB/Month vs S3: 0.15/GB/Month for storage. Curious to see if this is going to change. An extra competitor in this space will do no harm. Amazon has done a great job, but overall pricing can use some competition I think.

btw. during preview you get 100 gigabytes of data storage and 300 gigabytes of monthly bandwidth at no charge according to: http://code.google.com/apis/storage/docs/overview.html