This is an interesting product I've been playing with for this for a while now:
http://www.musicreader.net/
It allows play lists, comprehensive library management, annotation, partial and full page turning, syncing between various platforms (amongst other features) and there is an iPad version.

For a while I was unhappy with the page turning speed on my Win7 slate but this has improved a lot.

I find the sheer lack of size on my 11.7" slate and iPad to be a problem (guess I'm gettign older than I care to admit) but I'm looking at getting around that with this:
http://www.notebookcheck.net/Review-Acer-Iconia-Dual-Screen-Tablet.49679.0.html
Look Ma, no keyboard, but 2*14" screens. Will also all but eliminate page turn problems too.

I currently have 1500 odd PDFs in my library (some PDFs contain many hundreds of songs as well so there are far more than 1500 songs in it). Navigating large PDFs isn't the best because of processing speed in the slate (it is only an Atom 450), but navigating the library when all the songs are separate PDFs is a breeze, and setting up the play list is easy as.

At the moment I use it exclusively in church, but when I get the Acer I'll start using it on other gigs too, though the Acer will be no good outside.

BTW, I am in no way asociated with this product other than as a user. Marco, the creator, is very responsive, but English is not his first language so it helps to be precise when communicating.

--=-- My credo: If it's worth doing, it's worth overdoing - just ask my missus, she'll tell ya laugh --=--
You're only paranoid if you're wrong!