Let's do some simple math, shall we? Let's assume that Evan was the ONLY miner for the first 500 blocks (that's the worst case scenario... you can't assume he mined more than 100%). If we simply determine the network hash rate for the first 100 blocks (using the networkhashps command in the Dash wallet), you can see that there was only 12.6kh/s... this is clearly one (very weak) CPU and the first 100 blocks were mined in a few minutes... it probably took some time to add the other machines he and his friends had at the ready. But from blocks 100-500 the average jumps to 711.2kh/s and appears pretty steady that whole time. Let's assume that this 711.2kh/s is Evan and his friends. They would have gotten about 245,000 of the first 250,000 coins mined (through block 500).
By block 500, things start to change. A few others are clearly joining them by this point, but assuming the 711 of the 895 kh/s were theirs from block 500-600, then they still got 79% of those blocks too (worth about 40,000 Dash). If you repeat this process to figure out the share of each block of 100 they got, you get something like the following:
EDIT: The coin start and coin finish are the beginning total coins in circulation and ending coins in circulation for each set of 100 blocks... so the difference is how many were created for each 100 block section... multiply that by the dev's share and you can see where I get the numbers from.
http://imgur.com/Se5USkwEach row represents 100 blocks. As you can see, by about block 1,000, the hashrate was up dramatically... this is consistent with posts on BTC of many other miners saying they were up and running. There are a couple of points at which network hash drops, consistent with the fact that a couple of bug fixes went out which probably caused Evan and other miners to stop mining for a brief time to update. By block 2300, Evan and Co's share was probably less than 1% of the network hash rate, by which time these estimates would put them at about 511k coins. After that, there is little chance they got a decent share... maybe another 6,000 coins for the next 1,000 blocks, but basically the party was over by then, so to speak. So if you assume they got about 518k coins by the time they were consistently getting less than 1% of the coins, that represents less than 8.8% of the current number of coins in circulation... which is very consistent with the statements from Evan that "all of the founders" hold less than 10% of the current supply combined.
These assumptions are generous to the "instamine" haters for several reasons:
1) It assumes that Evan was the ONLY miner for the first 500 blocks, which we know isn't true. There was at least one other developer at that time, I believe a friend of Evan's, but I'm not sure... so the "instamine" would have been split at least between two people
2) It assumes no one else was mining for the first 500 blocks (which may be the case... we'll never know, but I make this assumption in the interests of being conservative)
3) It assumes that Evan and Co had absolutely no down time for updating their miners, which is impossible... any downtime would reduce these assumptions
4) It assumes that once huge amounts of mining power joined beginning at block 500 that Evan didn't start experiencing an elevated level of rejects... this is unlikely as well since blocks were being created so rapidly at that time - literally seconds apart on average - that he and many others reported rejects, getting on wrong chains, having to reset, etc. Evan would have no way to be immune to these issues caused by the rapid creation of the blocks and network latency, so the true "networkhashps" is clearly understated during that period because many blocks were rejected and not counted.
5) It assumes that he never sold any Dash
Based on the data, I see no reason to disbelieve Evan and the stated amount of coin that he has. In fact, the data seems to support everything he's said.
I made one meaningful error in this post that I'd like to correct, since I see that many other people are finding value in it and referencing it...
If you exclude the genesis block from the calculations on the first set of 100 blocks (since there is a time lag between the genesis block and actual mining), the hashrate average for my first set of 100 changes significantly (and the associated assumption that it was just one PC is no longer valid). Excluding block 1, the next 99 blocks averaged 395kh/s, NOT 12kh/s. So the first 100 blocks were clearly NOT mined on a single PC. This introduces further (though not much incremental) doubt that Evan was the only miner for the first 100 blocks. It was certainly more than one machine, though.