I wrote and ran an arbitrage tracking site for a few years and eventually stopped because there did not seem to be viable way to take advantage of cross-exchange spreads. Sell-Move-Buy didn't work because moving coins took days. Having a pile of each kind of coin on each change is fast but defeats the point of arbitrage because the pile itself it subject to the price changes that arbitrage is made to avoid.
The chart below shows the result of looking at the orderbook of different BTC exchanges, seeing how much was actually offered at a winning price on other changes, computing the total, and taking into account exchange fees (more or less)
At 10:10pm there is a $16USD spike - probably between BTC-E and Gemini that lasted a short while (refresh rate was every 10 min)
I always thought the code could be generalized enough to look at any number of exchanges and coinpairs. I'll keep an eye on tokenspread, it looks like a good start!
What's pretty cool about this -- though it appears this site is not focused on it -- is the opportunity for full triangle arbitrages among the various crypto's, such that you may do, e.g., a BTC->ETH->LTC->BTC trade and wind up with more BTC than you started with.
Another point to consider; the big players have moved into this space, if you want to get into it you will need to be sure you're not at an informational disadvantage.
I'm was actually surprised BTC-E didn't do something like that themselves, since the they don't have to pay any transaction fees, and they also had zero lag. It's like free money.
Usually the "opportunities" in arbitrage that sites like this highlight ignore the fact that the targetted coin on one of the exchanges has abysmally low volume, so you'll be unlikely to be able to buy and sell it in time to take advantage.
Other gotchas include: time to transfer the coin between exchanges, fees involved (both in transfer and on the exchanges through buy/sell fees), and exchanges where deposits and withdrawals aren't fully automated (some Chinese exchanges were like this).
 change bitcoin to coin
Exchange transaction volume should also be fairly readily accessible, but I'm not sure about that. This could be used to calcualate a probability of success to also take into consideration.
Even the various World of Warcraft auction house arbitrage add-ons take this type of stuff into account.
It feels like talking to a stock broker / investment advisor who gives all the numbers while leaving out any mention of their cut. In this case the Token Spread site doesn't seem to get anything out of it, unless they somehow tie into exchange affiliate programs wherever they link them up.
I don't understand. If there's an order in the order book on the sell-side of one exchange that matches one on the buy-side of another exchange, what does volume on either exchange have to do with the ability to take advantage of this situation?
Example: a few years ago there was a difference of a few hundred dollars between U.S. and Chinese exchanges. But you couldn't really trade on the Chinese exchange unless you were or knew someone who was a Chinese citizen.
I haven't researched it, but my impression is that arbitrage is only indicative of market inneficiency. And a corrolary is that by the time you get into a position to take advantage of significant arbitrage, someone will likely have beaten you to it.
In other words, efficiency is antithetical to arbitrage. I welcome alternative perspectives.
There were public order books years ago and there were still arb opportunities because the field was niche and people just hadn't written the software yet. In terms of your comment, the technical barrier was what "average investors cannot efficiently surmount." At this point the high-volume pairs are too crowded but I suspect that there are still opportunities to make money where technical complexity is still high (e.g. smart contracts).
Taker fees should be shown on all of these potential cross exchange arbs. Exchange withdrawal fees should be presented somewhere as well.
For those looking at this site and seeing the percentages and thinking it's easy money, it isn't. Arbing has become a pretty crowded space and this kind of low hanging fruit is very hard to capture even when fully automated, not to mention the banking logistical issues of using USD (not tether) as a base pair.
If building trading systems in the crypto world is something that interests you feel free to reach out to me, company / contact info is in my profile.
All I want is just one "arb opportunity dashboard" to show the whole picture so people don't think they can deposit some btc and start clicking away generating a profit...