I play the Old Indian. One of the first chess DVDs that IM Andrew Martin ever did was on the Old Indian, it was Foxy DVD #6 "Anti-Flank", and Martin explains how you can use the Old Indian against all flank openings. This was a godsend to me since I often play against Rybka 4, and it opens with c4, Nf3, and g3 just as much as it opens with e4. It was nice to have a system to use against all of them so I don't have to spend study time on theory.
The only thing is Martin recommends blocking the center with c5 if White plays d5 but another more active idea is to play a knight into c5.
There's also something called the Janowski Old Indian where you play an early Bg4.
The New Old Indian book is pretty good too, though it really only covers using the Old Indian against 1.d4. Also that book is kind of advanced. I've only skimmed through it.
I think the people who play things like 1.Nf3 1.g3 1.b3 1.c4 etc are trying to make their opponent feel uncomfortable by taking them out of their main e4 and d4 openings. That's why the Old Indian is so good, it gives you a general development plan you can use against all of them based on getting a pawn stake at e5. You can actually feel your opponent's disappointment when he sees your purposeful development in the face of their vague opening, like they're thinking "ah no, my stupid 1.Nf3 move isn't confusing them like it does to everyone else".
Also people say it's a stodgy opening but I've had some great tactical games, and one game Martin shows in the DVD is him vs I think it was Wolfgang Ullman, but he ending up getting a kingside attack and winning in fantastic tactical style with a killer interference move.
The old indian is annoying. It's so equal and drawish when you allow e5 unopposed. Generally a good idea to make it slightly more difficult for black is Nf3-Bf4 and other more indirect ways if they still persist.