Don't know if this issue has been already brought up, but as I understand it, there is a problem with SolidCoin retarget algorithm that will manifest itself when the difficulty reaches the hashrate. Since it considers only the last 240 blocks when retargeting (correct me if I'm wrong), there will be huge fluctuations in the difficulty level. I ran some quick simulations, and you can expect the difficulty level to regularly fluctuate between +-20% where it "should" be, and more than that in some rarer cases. So every once in a while, you'll have situations, where the "real" difficulty according to the "real" hashrate should be 10000, but SolidCoin target is actually 12000 and drops to 8000 with one retarget (33% drop), and all this while the hashrate is static.

It's certainly not a showstopper, but hardly what I would call optimal, and something to consider if you are planning on copying retargetting from SolidCoin for your own project.

If I were to design a retargetting algo, I would find the first block that has a timestamp a certain amount of time in the past (say 2 weeks), see how many blocks were generated in that time, and adjust accordingly and often. Not the other way around as it's done in all current chains.