Generally Android and iPhone users are directed to touch.facebook.com while most other users are directed to m.facebook.com, now that the sites are merging there are going to be people that are worried they'll get a restricted or downgraded Facebook experience. Fear not! Facebook Head of Mobile Products, Erick Tseng explains that up until now having two versions of Facebook's mobile website led to issues.
The site's engineers were having to rebuild the same features twice, leading the two sites to rarely reach feature parity. Facebook is now launching a new framework built around XHP, Javelin and WURFL that uses the same underlying codebase, while tweaking UI elements on the fly depending on what device you're accessing the site from.
This makes life much easier for Facebook as their engineer's will only have to implement a feature once on their back end and if your phone supports it, it'll work all fine and dandy. Facebook is also now optimizing graphics on the fly - this is visible by looking at the Share button in the picture below: