Weed can for sure fuck up your game. A lot of it depends on the type of weed your smoking, but more importantly what your personality/mental state/and the way you react to it. There are some guys who smoke plenty of weed before going out, and it doesn't fuck up their game, these guys' tend to be good looking, "naturals", with high confidence and good "inner game".
A lot of times weed will make a person who is naturally introverted (like myself) even more introverted and in their own head. For people who are not that confident, and have "social anxiety", smoking weed can make them feel really anxious, uncomfortable, and more than anything "self-concious". Needless to say, all those things are major game killers.
As far as types of weed, outside the west coast or Colorado most of you guys are just smoking whatever you can get. If you're luckier you'll have a wide variety of herbs to choose from. The rule of thumb is that indicas are super heavy, stony buds that are good if you just want to chill in, watch a movie, and eat a frozen pizza. Sativa, on the other hand is way more of an "up" high and is better if you want to get out of the house and do "stuff." Sativa would be a much better option to smoke before/during social situations.
To touch on the weed and motivation subject. Yes weed can severely affect your motivation (I am a perfect example of that), I'd like to think that I'm a highly intelligent person and moderately successful, but I'm lazy as fuck and I know that I waste a lot of my valuable time being stoned (like I am right now as I type this), time that I could spend actually working, accomplishing things, cleaning/organizing, reading, planning moves/ideas/strategies, etc.
If you're on the fence about going out on a Wednesday night and you are already feeling "mellow" and you take a fat bong rip, I think you're deciding your fate at that point... Munchies, "It's Always Sunny in Philadelphia", and a possible xhamster whack sesh before you pass the fuck out... Not knocking it or weed, but if you're intent is to go out, be social, "run game", and try to pick up women, smoking weed is not a great plan.
Now, I burn herbs all day, but I try not to smoke anything at least 2 hours before I go out. When I go out I focus on drinking. I got a good homie who always tokes a blunt in front of the bars. I will usually hit it once or twice, but I don't want to get too stoned. It's important to have a good alcohol buzz going before you toke any ganja, because you want to enhance the feeling of the booze, not the other way around. If you smoke more at first and drink later, the alcohol will be enhancing the weed high.
Final notes, recently I roll to the bar with a little doobie twisted up. I save this for at least 2/3 of the way thru the night when I got my drink on and buzzing off that. I will either use the herbs as an opener a la G Manifesto, and ask some cute girls in front of the bars if they want to smoke. Or I will use the joint to try to get a girl(s) that I'm already taking to to step out and blaze with me as a way to isolate, build comfort, etc.
No go forth and smoke some ganja, but not too much that it fucks up your game!