Do URL shorterners pass page authority?

This is something I’ve got to experiment with: do URL shorteners like TinyURL and bit.ly hurt a targeted page’s authority? And if they do intercept the authority, is the added traffic they drive worth the loss?
Services like TinyURL are extremely useful for sending pages with long URLs to people over e-mail or Twitter, where you only have 140 characters. But bloggers use them, too — because shorter URLs are just easier to deal with.
But how do those services redirect the traffic? When search engines find TinyURL and bit.ly URLs on the Web, where do they assign the authority: to the TinyURL URL or the underlying page? Because I don’t recall seeing bit.lys or TinyURLs in search results — and I look at a lot of search results — I suspect that they pass the authority just fine. But it would be a big deal if they didn’t; a few good backlinks can be difference between a non-existent search position and an excellent one.