ReSiever - 8:20 am on Mar 18, 2005 (gmt 0)

I suspect it has something to do with gathering data for a forthcoming major update to Google.

Could well be. I also haven't seen it requesting .js files, so im not worried about that. It follows links between <script></script> tags, but the normal Googlebot also does that, so thats not something to worrie about.

But i also suspect it's analysing content much more then the normal Googlebot. I have a few pages behind my site which don't have much content on it, but are used as seopages. No bad things in it, just optimised for some keywords.

I had the pages visited by the Mozilla spider in januari and actually thats the last visit i ever had by Google. Maybe it determines the 'usefullness' for the actual spider, based on the content it analyses?