It's not really in keeping with the dynamic preferences of modern chess praxis, but perfectly sound and very playable.
Definitely a great lazy man defence. I can't understand why I've never played it! 
Old Indian Defence
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Right! I think it is playable against most non-e4 stuff and that is even without quoting that antydning gods below master level.
It's solid and playable for sure, but i don't think that it's a terribly easy defence to play. It's one of those solid setups where black looks in decent shape after the opening, but then his middlegame plan is not that clear while white has obvous ways to improve his position. If black decides to just trust his solidity and stay passive he invariably gets squeezed to death.
I'm not in any way suggesting that the OI is bad, just that it requires little theory but deep understanding and a good sense for counterattacking at the first chance after patiently regrouping for many moves. These are uncommon qualities below master level, an i don't think it's the ideal defense for an amateur.
By the way have you ever seen the famous game Averbakh-Kotov 0-1 (Zurich 1953)? If not you should immediately give it a look, It might be considered the Old Indian immortal :)
Is it any good? A solid candidate for a lazy man's Silver Tape repertoire?