Yeah that's happened to me, it's cool to know it's a Ditto, that way you can cut to the chase and use a Great Ball or something. Asshole Pidgey still ran away from me though, my brother in law caught him and got a better Ditto.
At this point I'm betting they'll roll out Gen 2 in time for the holidays, though I'd also like if they made some rarer Pokemon from Gen 1 more available during that time, since there are some, though many players around here have them, I've never seen in my neighborhood, such as Snorlax. I dun really have the time to go into Manhattan to find things at the moment.