I've slowed down, got almost 50km on my tracker but I've caught everything that's likely to show up where I live and it's not as much fun anymore. The gym system's pretty barebones and as someone else said the complete lack of entropy means you fall behind really fast. We're already seeing 3000+ guys on the local gyms.
And even then that doesn't mean anything because six 900+ dudes can take a 3000 and wear his gym down. So what's the point? Your gym will change hands within an hour if you're in a place with any population at all.
I've been playing PU on pokemon showdown lately. It's a lot of fun, very different from OU. The main thing that happens as you go further down the ladder is the pokemon become less consistent and the gap between the top and bottom of the bracket gets wider.
Like the difference between the top of OU, shit like Lando and Talonflame, vs the bottom with guys like Beedrill, is mainly just splashability. You can throw Lando anywhere, Beedrill can be just as good he just needs more support.
Not as much in PU since it's the bottom of the bottom but in RU and NU you've got a lot of pokemon that are really good but just outclassed. Moltres is the one I keep bringing up, mega sceptile when he was still RU. So the lower metagames are really centralized.
PU's just weird. All the good shit is so weird, it's really fun. I kind of want to take a banded or life orb raticate into OU some time and throw him in on a will-o-wisp. I guarantee nobody in OU will see that shit coming.
Drifblim is also really fun. He's got unburden and acrobatics so you give him a Liechi berry and try to switch him on a weak attack and then substitute. He'll blitz weakened teams and he's got a great bouncy warcry.
The number of weird, one-note pokemon does mean there's a lot greater volume of dumb shit in PU. Expect lots of two turn games when you counter his stupid gimmick and he immediately forfeits.