We found the same thing when we started pulling web.UserAgent data into InSite for Jive. Jive's implementation seem to be a little wonky, even though web.UserAgent is supposed to be somewhat of an industry standard. The other issue is that the field is an array field, which means the data is all smooshed together, like the Profile field that contains all the custom profile fields. We are working on a way to parse this data somewhat consistently into separate fields (OS, Browser, FormFactor - for instance) but we are not there yet. Totally not surprised that you got 750 agents in just 2 weeks.
If they were more structured in their smooshing, it would have been easier to de-smoosh . Thanks Ben - can't wait for you to solve this one too!