I've always suggested 5% in the past, but now I actually think 20% is decent(but yes, still risky as hell). But then again, it really completely depends on the person's financial situation.
What one's investment strategy would be if I were a fresh arrival is a very interesting question. I really don't know how I'd approach it now. There's still plenty of risk. Who knows how much short/mid term upside there is?
I'd probably be looking at several years out rather than trying to catch the next bubble. In that case 20% would feel like too much but I'd also be conscious of 5% producing a pretty piddling gain. As ever you have to balance the prospect of ruin versus it flying away without you.
We may be about to enter an interesting phase where many will be asking themselves the same question. It's way bigger and more established than it once was but it's still too wild for boggo investment however many will also feel they missed out on the really stupid gains so will shy away from it.