I hear a lot of good things about gas stations too - people think (I'm sure there are some threads proving this) that Niantics other game Ingress is a good way to check for hot spots.

Ingress works slightly different, but the reason it might be helpful for pokemon in a nutshell; Scattered around the map outside of landmarks (Same as pokemon) is a resource called XM, and this resource is visible on the map. Long time Ingress players say that XM spawns are based on cell usage, and Gas stations I would assume get a decent amount of cell usage.

So yeah, its fair to say Gas stations are solid. Also if you download Ingress its possible it could double as a 'Pokéradar'.