[snip]
It's easy to underestimate trading volume. Do you have an evaluation for total Ripple 24h trading volume?
BTW I'm more than sure, it is underestimated for many other cryptocurrencies as well, including Bitcoin. So, do you think, Ripple market cap is indeed somewhere between Bitcoin and Litecoin?
P.S. And do you think Ripple market cap was higher than Bitcoin market cap during last summer, when exchange rate was like 5000 - 8000 XRP/BTC?
I am not too sure about trading volume (haven't gotten around to collect enough history on my ripple server yet to do "real" historical analysis), the situation is a bit similar to MtGox who in theory trade a lot of currencies against BTC but in practice most of the action is in very few markets. Also it is very easy to create your own little market on Ripple with bogus values (you could issue yourself BTC and trade back and forth with near 0 fees), so it makes sense to only consider certain markets that fulfill certain criteria (whatever they are).
Bitcoin has similar issues by the way, just take a look at some chinese exchanges with trading volumes several times above the ones at MtGox or Bitstamp...
About the market cap being indeed that high I'm quite sure, as even few trades are enough to see how much people are actually willing to pay for one unit of currency. It might be debateable of course if that is a good measure, in the end however this measurement is what this very page does and advertises.
About the postscriptum: I'd have to check, but if you just do the naive 100 billion / 21 million calculation that would mean that at ~4800 XRP per BTC the cap will have to be higher. Since there are only about half the BTC available so far, this number will be about twice as high, so any rate below 100 billion / actual_amount_of_BTC means XRP have a higher market cap. This was very likely the case last summer.
100%+++ 
