I've only used SY once, and that was for a trip DCA-MSP. Basically, I was down to SY or a hidden city on DL as my choices (since MSP is stupidly expensive for DL) and SY won out.

I'll say that it was a very good airline for being a "lower-tier" carrier. F was reasonably comfortable (no IFE, which I found to be a plus, especially since I was traveling with a friend) though perhaps a hair out of date. Staff gets good marks all around...it reminded me of the good attitude, etc. of People Express (the PHF-based one from a few years ago) on their first flight.

I don't think I'll have much of an excuse to fly them again...I don't generally have a reason to visit MSP and their hard product falls behind that of VX or higher-end DL...but I've still got plenty good to say about them.