When i GM i have my players run their characters by me before the game and really just check to see if their sheet matches their character. So 7 in a stat wont really break the game but i have in the past made 8 the minimum. But the best way for characters with low stats is to make sure that it IS an issue for them in game. It adds to roleplaying and brings out the character flaws as well and if they did it just to min/max it can be seen as a punishment. For example take charisma, a character who dumped his down to 7 (or 5 post racials) makes a really compelling speech to sway the mind of a potential employer I would ask for a diplomacy check (DCs of these checks depend on how compelling the arguement or statement) now his dump charisma becomes a serious problem. I also dont allow metagaming on conversations so they cant just tell the other person in the group "Hey ask him this" while standing in front of them.
Alternative Solutions to dump stat players as a GM:
Physical stats show with exception of dex,
Strength: Enforce carrying capacities/NPCs may comment or pass over a pc for a task because they look weak.
Dexterity: Require them to make dex based checks that are auto successes for other players/Comments on how they have no coordination (they pay for this one with their reflex save anyway)
Constitution: Between their con score and HP, this one doesnt need further punishment/ NPCs may comment on them looking sickly or meek passing them up on jobs they dont think they will survive.
Mental Stats dont show as much but become obvious:
Intelligence: Not so bad mechanically their lack of skills will suffer, but be more inclined to make them roll to identify monsters or recall information. "Hey i dont remember what did NPC Jack say" me: "make me an int check". Set at an easy DC or so./NPCs may ridicule the player for being stupid. Intelligent NPCs may not care to speak to him. Overall not terribly bad on the RP side. Also consider making 7 int illiterate trait if you want to. He cant read or write.
Wisdom: Low will saves, perception checks and sense motive. also must make perception checks more frequently maybe leave something out of a description until he rolls./ He will likely come off as witless to other npcs unable to perceive their social ques. No common sense or a special needs character.
Charisma: Everyones favorite dump. Force diplomacy, bluff, and intimidate more frequently than for characters that do not dump. Do not allow metagame conversations./NPCs may react to this character with extreme disgust and generally find his presence annoying. Even if he says something great his personality (expression, tone of voice) might cause him to be ignored. He may have to roll diplomacy just to get people to talk to him for extended periods.
*a higher charisma with a lower intelligence or wisdom can counter this RP social aspects in most cases. Think dizzy blonde who can talk her way into or out of social scenarios.
I think with guidelines kind of like these ones it will allow characters with lower rolls but have them know that it will come up in the game at some point where low stats will be an issue. It could be fun to roleplay a character who is challenged in some way but generally it will encourage a more even distribution of stats.