One of calibre's lesser known features is that you can set it up to act as a content server. Run calibre on a computer and other computers on the same network as that computer can access the ebooks managed by calibre. This usually works through a web browser, and it can work over the web.
If you have an Android tablet on the same network as the computer running calibre, you could use the tablet's web browser to access the calibre library. Or, you can install this app and do the same thing.
Yes, the app duplicates something you can already do in a web browser, but it also does it very well. I've played with it for a few minutes today and it's a pretty good app. It can sort by author, title, publisher and other categories. it also has a search function as well as quite a few settings options (password, download folder, several themes, etc).
But it's also selling for $3 in the Android Market. I'm not sure it's worth it. Now if this were a complete port of calibre, then I would definitely pay for it. But as an auxiliary app...