I've been in Toastmasters since 2004.
I originally joined because I often find myself speaking outside Toastmasters and wanted to do a better job. I was initially skeptical that 7-minute speeches would help much toward multi-hour presentations -- but there's no question that it's helped me a great deal. The key is getting lots of practice.
It helps to belong to a good club that gives you lots of speaking opportunities. My home club is Coherent Communicators, where I'm VP of Education. (If you're in Silicon Valley, come check us out! We always welcome guests and prospective new members.) I'm also a member of GeoSpeakers. I've earned an AC-Silver and oCL.
Finishing up your CC and wondering which manual to try next? Read my admittedly biased Review of Toastmasters manuals.