I just noticed this thread for the first time today. I like the idea of a spring-loaded ring to control the various modes, especially if it can be easily operated with a thumb. However, I am not generally a fan of stateful controls like this. That is to say, I prefer controls that do exactly the same thing every time you press them, regardless of what mode the flashlight is currently in; if different actions must be stacked into one button, I prefer that they be simple and closely-related. (For example, I am fine with the same button being used to power the light on and to power the light off).
Does anybody know of a light with a spring-loaded ring like the Spartanian II, but with more than 2 positions for the ring to lock in to? For example, there could be an arrow on the ring which you would line up with markings on the body (e.g. "off", "low", "high", "strobe", etc.) to set the current mode. Thus, you could see immediately which mode it's in (particularly useful on a driver with many modes -- e.g. "did I leave it on 90% or 100%?"), and it would pass Theatre Booth Guy's "loan it out" test.
I'm no electronics expert by any stretch of the imagination, but I suspect this would also make for cheaper electronics, since the modes could likely be implemented without a microcontroller, since the ring would essentially be a switch with many positions of throw, rather than a momentary (on)/off/(on).
BTW, to be clear, I don't mean the above as criticism of the Spartanian II -- its design just got me thinking about rings as a flashlight's UI.