also, that interval: 500 was a typo... i did the math right in real life.
;-)

oh, and don't forget to change this line:
if (Time.now.to_i - last.to_i) > 120 || last_twitter == ''
to this:
if (Time.now.to_i - last.to_i) > interval || last_twitter == ''

it would be nice if you could edit the frequency of updates in that YAML file. I've now got at least 7 apps hitting my twitter acconut, so being able to set it to like 5 minutes would be rad.

for now, I've just updated my local copy to poll every 5 minutes.

in ~/.twitter
i added:
interval: 500

in ~/Library/Application Support/Adium 2.0/Scripts/Twitter.AdiumScripts/Contents/Resources/twitter.rb
i added (just before the following comment halfway through the code: #store last twitter and timestamp):
begin
interval = (config["interval"] == nil || config["interval"] < 120) ? 120 : config["interval"]
rescue
interval = 120
end