Is there any available information of the type of storage Google uses for storing the original photos uploaded to Picasa Web Albums? Is it comparable to enterprise grade cloud backup solutions?
From their Google Data centers website:
Rather than storing each user's data on a single machine or set of machines, we distribute all data—including our own—across many computers in different locations. We then chunk and replicate the data over multiple systems to avoid a single point of failure. We randomly name these data chunks as an extra measure of security, making them unreadable to the human eye.
So, your data on Picasa Web Albums is quite redundant and you don't have to worry too much about the data getting lost. Comparing it to enterprise grade cloud backup solutions, I rather you keep your photos only on Picasa so that you can have a sense of security and privacy (and that third party companies don't have access to your data).