It's been, let's say, interesting. I've learned a lot about the lower level workings of TCP/IP, SYN and ACK signals etc and how they can get delayed but not ignored (part of the protocol design).
But I can't say that I've found anything particularly useful just yet.
I'm actually tweaking a TCP/IP based application which isn't for the web. I thought of asking because of course HTTP servers are essentially TCP/IP based. I'll take a look at Yslow though - there might be some useful config tidbits in there - thanks for the heads up.