Since the single biggest discovery through Tiger has, for me, been RSS feeds (which, admittedly have been around for a while) I wondered if you could refresh the feeds, so when you get home and want to see which ones have new stories you wouldn’t have to wait for Safari to check. Turns out the update frequency is 30 mins although this can be changed. However a forced refresh (like forcing mail.app to check for new email) doesn’t seem to be possible.