Thumbies rule!
I'm running the original Suntour Power Thumb friction shifters, circa 1983. Best shifters ever, most people won't part with them for any amount of money. I was lucky: LBS recycles a lot of old bikes and had one lying around in his backyard, I swapped him a case of beer for it. Simple to set up and you basically never have to worry about adjustments. I'm running an 8-speed cassette, single front ring.
I'm also hoarding a couple sets of index shifters: a set of used XT 8-speed thumbies and a set of NOS 6-speed Suntours, in case this guy bites the dust. I somehow doubt it -- this is a totally bombproof unit that has been going strong for 25 years now.
I'll admit that other shifters are more effective when it comes to actually shifting, but I want something that doesn't need adjusting all the time and will get me home when I'm 50 klicks out in the bush. I hate that plastic crap that passes for shifters nowadays. I'll live with the downsides of thumbies.
Oh yeah, thumbies are also a big plus when temps hit 40 below and you need some serious mittens:
Try shifting your rapid fires with those babies on your hands!
Regards,
Anthony