This is a rebuilt version of an enchanting library I made on a server a while back that allows you to cycle through 4 different levels of bookshelf -> enchanting table input. It might be a little overkill for 1.3.x since the experience level cap is now 30, but it worked really nicely in 1.2.5 when you could go up to level 50.

Schematic saved using Schematica by Lunatrius. Learned to use binary counters in Goklayeh's Redstone Lab.

Edit: I may revisit this for 1.3.2 to make it finer-grained since the number of bookshelves required for max enchanting is only 15 now. Is anyone interested in an update to this for 1.3?