Meanwhile, why not try throttling it yourself? 5 seconds between requests would space things out a bit.

Since the techs haven't mentioned this limit before, and I'm 99% sure they haven't just added it, it looks like you have just exceeded the limit now.

It is set at 5 seconds (but you would want to pull at a slower pace in case the timing between each request had some variance).

And yes - we had to add this on Tuesday morning. We had someone pulling a the stats via this interface at around 6-7 requests per second and that caused the website to lock up for about 2-3 hours while we figured out what was going on.

I will drop the throttle down to 2.5 seconds. This will take effect when we release the next major release of the website (in about 2 weeks)

It sounds like it would be more efficient for everyone if WCG could provide, and document, an HTML servlet which would accept a delimited list of tags and return an XML document with a row of values for each tag.
This would allow the different signature providers a documented mechanism with a hopefully smaller WCG bandwidth impact than current techniques.
Yes, I realize this is an enhancement which someone has to code, and there may be some security/privacy issues to consider, but I thought I would suggest it.

Mousie, could you easily take a "round robin" approach? Send a request to each project rather than all requests for a given project back to back? You could set a time flag each time you send a request to WCG and the next time you need to send a request to WCG, check that and throttle if necessary? That might help keep down the total time for your stat updates. Just a thought.