Some time ago I posted about avoiding abbreviated urls (such as from bit.ly) for Tweets. The reasoning being that the links from bit.ly won't receive any SE love due to the nature of the linking platform.
There was an oversight on my part as I didn't realize to check on the nature of the links on the Twitter homepage, they're all marked with rel="nofollow" -tag, which makes the whole point moot.
There are some nice tools for showing the rel="nofollow" -tag on the browser, for Google Chrome there's Nofollow Checker, for Firefox there's the DoNoFollow which both subtly indicate on screen which links have been marked up as no-follow links. Unfortunately, I've yet to come across a similar one for Internet Explorer
