i'm not sure offhand how the 1 button mice work in OS X as my last venture w/ a 1 button mouse was before then and i currently use my (19,0000 button) logitech mouse w/ the iBook. in any case, if i remember right, old school Mac mouse-use, used to basically have multiple functions built into the one click. so for instance if u were on a web page instead of right clicking on a link u could just hold the click down and the "right click" menu would come up. so basically it was more of a quick-click vs. click-hold for different functions.
everybody bitches about the 1 button solution on Macs, yet on my old compaq laptop i found that i felt inefficient in my trackpad use when i had to curl my thumb under my hand as i needed to keep my index finger on the trackpad for moving the cursor down a potential drop down menu, and that corner touches felt more ergonomic (i.e.-using bottom right corner for 2nd mouse, as i do now on the iBook). on my iBook i tend to have both hands front and center, with my left thumb hovering over the command, alt, and ctrl buttons, so in the need of any of them, for me, it is arguably easier than the one-handed-curling-thumb-under technique of the 2 button trackpad situation.
in a desktop situation i can see where more of the 2nd mouse button anxiety comes from (bc u can't thumb yer butt w/ the left hand while being free to navigate w/ your right hand. jk
). at the same time, i basically know that i'm being lazy when i don't want to raise my left hand to the KB to ctrl+click on a link in firefox to open a link in a new tab in windows. long story short, if i'm "power using" in either OS, both hands are on deck for mouse and corresponding KB commands, so the whole argument of "u mean in OS X i have to use my left hand to press the ctrl button instead of right clicking?! gosh! idiot! <napoleon dynamite intonation>"-is kind of silly anyways.
so yeah, being a regular dual platform user, i can say i don't really think it's a big deal at all to get used to.