in '95 i took over running the Client / Server SIG, and in '96-97 i co-chaired the Internet SIG with Janice Carter (Janice helped teach me the very important lesson that it's incredibly helpful to run a SIG with at least 1 other person... Janice rocks).
in '98 i founded & co-chaired the E-Commerce SIG (which later became the Web Services SIG) with help from several other folks (primarily Molly Pengra), and in 2000 i founded & co-chaired the Venture Finance SIG with Kevin Hartz, just in time for the dot-com crash ;)
Running SIGs can be a lot of work, but it's also a lot of fun. You get to learn a lot about a subject of interest, you get to meet some incredible speaker and a bunch of geeks who share the same passions, and occasionally you may even get 15 seconds or so of minor fame (though not much fortune, since SIGs are run by volunteers). Tip: don't do it for the fame or the money.