It's probably only the log files.. if you have a version of solidcoin that doesn't actually crash on shutdown - it might tidy them up when you stop and start it.

I don't yet hold any confidence that the solidcoin dev will solve scalability issues though.  The solidcoin accelerated schedule and shorter block timing will mean that they will potentially run into file size, bandwidth and other scalability issues if there is any real growth in transactions.

It's possible the mainline Bitcoin developers will solve these issues and solidcoin can just copy that - but I know which devs I'd rather trust.

Still.. if solidcoin does run into some scalability issues soon, it could prove a useful dataset for Bitcoin devs to examine!