I'm a developer and last week I cut one of my clients site's live and put a 301 redirect on their old domain to point to the new domain. Today I got a Google Alert for a keyword I'm tracking for another client pointing to a forum post on the old domain. The cache for the page is dated 19 July so are Google Alerts just working through the new cache entries as they get added (I know there's a delay with them)? Sarah
Sometimes I see them right away, sometimes they are delayed. Some have come with multiple links in the mail, for content that had been put up or linked to on different days. Google is known to use less buzy servers for calculations when needed, and I think that is what is happening here. I know that there are links that I put up in the last few days and the pages have been cached - I am due an alert, but have yet to get one.
While most of 'em I see are pretty recent, I've seen a number from MONTHS ago - makes me wonder "what up" ;-)
Some of the content may be old as Google may take a while to index it. It's when the actual indexing is old that I was wondering about...