LibSDL is currently at version 1.2, and is indeed one of the coolest APIs around for cross-platform game/multimedia development. Certainly more working in Linux than certain other libraries were a few years back...
Personally, I chose SDL for my own little project lately for simple reason: It lets me to use OpenGL for 3D graphics, but it has considerably more advanced and more easily programmable 2D graphics primitives than OpenGL. (Fast blits and such...) I was noticing that it can also blit 2D graphics on OpenGL screen, which would be a great bonus because I lost several weeks worth of sleep trying to use OpenGL and GLUT for drawing simple 2D bitmaps on screen... =(
Basically, SDL is an equivalent of DirectX that can be - and have been - ported to other OSes besides Microsoft Windows. In the Great War between OpenGL and DirectX, people forgot that OpenGL is just a graphics API, while DirectX has all sort of stuff including joystick reading, 3D sound, and stuff like that...
SDL can do following things:
Currently, it runs on Linux, Win32, BeOS and MacOS (including MacOS X).
Only specific problems I've seen - from user's point of view - has been that full screen mode may be somewhat buggy in X, but that's hardly news...