Your feed stats may have dropped significantly today. They may also have been very erratic over the past few weeks. You should find them more stable now. Let me explain.
When a large service such as Netvibes requests your feed, their request includes the number subscribers they are servicing for your feed. They do this by including something like "30 subscribers" in the request. Your feed stats are the sum of all of these.
In the months since we launched Feed Stats, aggregators have experienced explosive growth. When a service like Netvibes gets very large they start needing lots of machines to do the work, so these requests may start arriving from different machines. There may be as many as ten machines each reporting "30 subscribers" which makes it seem as though there were 300 subscribers. This was making your feed stats report a falsly high number of subscribers.
This problem did not exist when we started, and some large services are careful to keep their requests coming from a single IP. We still have to account for those that do not. This is a tricky problem because the solution involves a lot of guesswork. Each aggregator may have its machines anywhere on the internet, so we cannot make assumptions about IP subnets, e.g. 10.10.10.x. The opposite problem is also a factor: there may be several installations of an "enterprise" aggregator that appear to be the same entity but actually service a different set of subscribers.
A few minutes ago I updated the code to try to weed out the duplicates while respecting enterprise aggregators. Your feed stats may drop as a result. They may even crash. Unfortunately we cannot apply this change retroactively. On the bright side, this change means your feed stats will be more stable and accurate from now on.