I haven't done any testing for a while, but here's the way it's been historically. If the urls in the option elements are "straight html" (not generated through a javascript method) they can be used to discover urls. That is, if the url isn't already known to Google, they will use the url in an option to attempt a crawl. However, historically there wasn't any PR transfer or backlink influence through select options. It's not really a link, you see, but an input that could do all kinds of things once the script gets a hold of it.
If the links in a select box are important for the site, then I'd make sure that spiders have another path to follow in addition to the jump menu.
lorien1973
9:42 pm on Nov 13, 2007 (gmt 0)
You could just make the selection box an unordered list and use CSS turn "turn it into a selection box" for the end user.