Hi people, i am quite new to the Fallout series, just bought New Vegas and i have been playing it for about 25 hours, basicly i was wondering if it matters that i have bad rep with Powder Gangers, Fiend, and Scorpion Gang, i mostly mind my own business but if someone attacks me i will blow their heads off! so does it affect future game progress?
Thanks for your time
Actually reputation is important in New Vegas, far more important than karma is. If your reputation is bad enough with a faction, they will be all hostile to you. You won't be welcome in their areas, you won't be able to take missions from them and in some cases they will sent hit squads after you.
That said, you can't make everybody happy in this game. You will take some sides, or at least piss some people off. Knowing who to piss off is kind of important. The NCR in particular controls a fair bit of the Mohave, so making them angry at you will kind of severely limit the places you can go. Best to be good chums with Caesar's Legion if you do that.
The three you mentioned though are thugs, gangers and raiders, and don't have much pull. And as you've noticed a lot of them are hostile to you even before their entire faction hates you. So unless you are playing a run through where you specifically are siding with them to do their quests or what have you, it's not a problem.