I think the checksum algorythm used to request pagerank data from google by the toolbar is used for performance reason, not to avoid other to use these data. (To avoid other to use these data there is already the TOS)
Remember that the data are indexed by checksum ?
I think the toolbar compute it so the backend don't need to compute it itself.
Am I right ?
I'm impatient to see next release of the toolbar there is lot of hidden treasure in it.