Why did use SDL anyway...
I think SFML is way better...
SFML uses more modern and cleaner coding techniques, better looking documentation (if you consider external documentation valid), more convenient uses, etc.
SFML also provides a hardware accelerated graphics API where SDL is still based on software rendering and integration with OpenGL is a complete bitch.
SFML, imho, has already surpassed SDL in many aspects as a free multimedia library.
SFML is pretty much superior in just about every way.
SDL made sense back when 2D drawing was hardware accelerated. Nowadays you get better performance with 3D libs like OpenGL (which SFML uses). SDL's video is too slow for practical use. I tried using it before, it just didn't cut it. You pretty much have to use SDL's OpenGL interface (which is minimal -- you basically have to use OpenGL directly) in order to get any kind of reasonable performance.
SFML doesn't have that problem.
SDL also forces you to do all audio mixing in software (at least as far as I know). Which isn't as big of a deal, but still hinders performance. (EDIT: actually is this true? I just assumed you couldn't open multiple audio devices at once, but maybe I'm wrong?)
SFML doesn't have that problem either.
SFML also supports more common things out of the box, like loading and playing ogg files, reading png files, etc. You need add-on libs to get that done with SDL.
SFML also has a simpler interface, a nice OO design, and an active forum base you can go to for help. AND it's still being actively developed.
There's little reason to use SDL anymore. I say definitely ditch it and use SFML.