I don't look through other people's collections very often, unless they mention something about one of their Pokémon, in which case I'll take a look.
Surprisingly often actually, if I happen to be on someone's page at least, it's interesting to see what kind of Pokémon a person likes.
Only really go to check if they request a medal that require specific number of mons or need a specific set of mons since I gotta check while handing out medals.
I don't look very often. The only times I do like is when a user says they have a shiny or something really rare and I'd like to see it.
Not very often but these days I've been snooping in @Grimwave 's crazy collection of shinies to fix broken images.
Catch a Ditto! I actually used to check them frequently but now I go to check if any Pokémon images are broken and then try to fix them!
I only looked through the collections for one of the threads in the game corner that was “which Pokémon nickname do you like from the person above” but nobody has responded to it in a while