low cha in Fallout 1
Yes, there are a handful of poor reactions that a low charisma character will suffer. For example, he'll almost never get Tandi to tell him the story about the deathclaw (barring arbitrary save/reloads to make a miraculous CHA roll). However, all of those bad reactions together isn't really signifigant. For just about every remotely important conversation tree, you can lean on a high speech/intelligence stat to get you through. In FO1, charisma is utterly a trash stat.
Which is, of course, another major fix in Fallout2. Not only does a FO2 character need a decent charisma to pick up the (much improved) NPCs, charisma checks are also more important for key conversation branches (becoming a porn star, captain of the guard, etc). Fallout 2's trash stat then becomes endurance, which anyone but a brawler can lock in at 3.