No. As far as I can ascertain, the drop is attributed to Feedburner
not counting Google Reader subscribers for the day.
My reader count in Google Reader was 37 that day; Feedburner showed
Google Feedfetcher subscriptions as 4 (indicating that it was probably
counting subscribers via iGoogle, but not via Google Reader).
Sliiiight mismatch. And since Google Reader seems to account for
around half the subscribers to any particular blog these days, that
was probably it.
Here's a (very very) short article from ProBlogger on how to count
your readers through Google Reader directly:
http://www.problogger.net/archives/2007/10/15/google-reader-reveal-subscriber-numbers-to-feeds/
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http://www.spontaneousderivation.com/