I'm amazed at the speed. I just posted something on siftables and googled it with a combination of arduino in like 20 minutes and google throws up the same post back!
Maybe you got the timing just right?
bots never sleep 
Lefty
I remember back in the early days of search engines, google would often take several days to index new content, now its usually a few minutes.
The average for most of my sites is about once a week. Active sites, such as blogs and forums get scanned a lot more frequently. Also there are several site sending live feeds to google so they are searchable instantly. Some examples are facebook and twitter
Well there seems to permenantly be a googlebot patrolling this site so I suppose it only takes it a few minutes to read the post and get the search updated.
Mowcius
You can google "site:whatever.foo" then in the tools on the left you can select latest - it'll show you the most recent posts it has indexed the forum at the domain you've just googled.
It's frequent for pages with rapidly changing content.
Edit: Under ten minutes: " It's frequent for pages with rapidly changing content. " - Google Search