Hi Andy
I'm also seeing this on one of our own sites, as well as a lot of other websites in our own sector. From what I can see in webmaster tools, there was a big drop in the crawl rate around 21st of October for a few days and then the crawl rate picked up to normal levels within a few days. However, looking at the cache date of the homepage as well as other category pages, the date of 20 to 22nd of October seem fixed. But, newly added pages are being indexed. This is strange to say the least!
Maz
