If those sort of tweets get into search results simply based on "newest", you can be sure it'll be used extensively by marketers trying to spam their way into search listings.
FWIW, Twitter seems to be on top of the arms race right now. A little while back I was getting 3-4 spam followers/@-replies a day; over the past few weeks, though, I've had exactly two.
I am getting these almost every day now. Annoying at first, now I am considering using some other service. Twitter is too popular and popular services eventually become shit.
For example: http://www.google.com/search?q=san+francisco+halloween gives me a bunch of halloween stores
http://twitter.com/#search?q=san%20francisco%20halloween gives me a bunch of events (much more useful for me!)