Yeah, I know how you feel about the darn purple rats lol, but every one you catch will get you closer to the next level. I catch and send them on.. gathering Stardust at the same time, so not all bad. But yeah, there are way too many of them.
I have caught many while riding in a slow moving car if the poke ball keeps them on the first try. But move too far away and yes, they will puff away. I do hate it when I have a rare pokemon and I am not moving, but they puff after the first attempt. But that's the game...
My biggest (and only) gripe is the little NEARBY box. I never see any of the ones on the top row that are shown in the game. Never. Ever. I have tried the trick to make them come closer, by walking north till they move away, then going back 180 degrees to the south... then going west, then east. Never ever have been able to corner one. Even if it is close, it never pops up on my screen. I would love to use that part of the game, but am not able to figure it out and make it work. I have told myself to ignore it, but I can't haha.
But, I will say it is a lot of fun and I'm really absorbed in it.
I still need 69 more pokeymon's to catch to 'catch them all' I will never find them unless I travel the US. Maybe they will hatch out because I have gotten most of the rare ones from hatching 10 km eggs.