While learning (a little) Cantonese, I was annoyed by the fact that every initial [n] was converted to [l], so that the word "you", written
in guidebooks is universally pronounced
People would, if pressed, say that the pronunciation is "néih hóu", and that they were using "lazy pronunciation" (see Cantonese phonology). The sound-shift was common to words with initial [n]. It did not appear in the superficial list of cross-linguistically regularly observed sound changes that I saw on Wikipedia, which were b>p>f, d>t>th and g>c>ch. These sound changes are just voicing/unvoicing toggles and turning into a fricative, both of which are simple transformations. Initial n to l is just strange (and, possibly coincidentally, it relates the semitic and Indo-European words for "no").
I was wondering if [n] -> [l] is a sound change which is common cross-linguistically, whether it is directional (is it observed going the other way), if it is confined to the initial position, and more generally which transformations are known with what direction and probability.