Well, with a good DM and good roleplayers, low Charisma becomes a severe handicap.
In my current campaign, for a change, I'm a player (as opposed to DM) and even I react very differently to Charisma. My character has Charisma 14 and talks almost exclusively to the Charisma 15 cleric- we're sort of co-leaders. She pays lip service and just about acknowledges the Charisma 8 rogue, although avoids talking to him unless necessary. As for the Charisma 3 barbarian (that's right- 3) she barely even acknowledges him. Indeed, for a long while she even refused to let him into the party and is extremely loath to work with him. We infiltrated the mansion of the evil cult, and guess who was left outside ('We're not bringing that oaf in'). Low Charisma is a handicap.
When I DM, I go even more overboard. NPCs generally assume that the character with the highest Charisma is party leader and react appropriately. They set them the quests and the like, and pretty much ignore the 'grunts' of low Charisma (who they generally also assume to be stupid unless they are wizards or similar). Shopkeepers generally charge low Charisma characters higher prices and vice versa. And that's just the roleplay elements. Once one factored in the mechanical side of Charisma, with Bluff rolls and the like, only the most ardent dungeon-hack makes Charisma a dump stat. To the vast majority of campaigns, Charisma is required to make Diplomacy, Bluff and Gather Information checks. Neither is having one high Cha character good enough. Suspicious NPCs will grill the least Charismatic character to find the truth, even if most will just accept the word of the slick bard irrespective of his 'lackeys'.
Whoever said Charisma was useles?