JoeFriday, my view on camera meters is that there are two main reasons to want an internal meter, otherwise it is just unimportant. One reason is for automatic exposure, which I rather like, especially useful for rapid changes in lighting. The example I recall was at Seattle's Pike Place market (um, 35 years ago!). On the street corner just outside the market there was some political soap-box speechifying that generated some emotional opposition. As I was shooting away, one heckler slugged the speaker, and the tussle moved into the much-darker market area. I cranked the lens open three stops and kept shooting, but I still underexposed by a couple stops, unfortunately. AE would have done well there, or maybe I should just get better at judging light change. BTW, I was using an M2 w/35mm and a Spotmatic w/85mm.
The other reason for an internal meter is for SLRs only, where TTL metering is really useful for macro shots where there are exposure effects due to lens extension, and also when attaching various filters to the lens.
Other than these reasons, I'm pleased to use a separate hand-held meter, mostly in the incident-metering mode. I think it's well worth noting here that once you know what the meter reading is for the light you have, there's no need to keep metering for every shot. When you suspect the light is different than before, check the meter again. This is a fine way to learn more about light and exposure, and what the meter is really telling you. You'll also develop a sense of what is reasonable, and use that as a credibility check when assessing the meter's reading.
Indeed, it's surprising how well one can do just following the exposure recommendations that come with a roll of film, or the cardboard exposure calculator Kodak offers, which are just based on the "Sunny 16" rule: In sunlight, your basic exposure is f/16 with the shutter speed set to the same number as the film's ISO speed. Shade and clouds of various degrees call for set amounts of increased exposure from the Sunny-16 baseline. Indoors is more difficult.
One other point about hand-held metering, and leaving the exposure the same until the light changes... Your negative sequences at the same exposure will be pretty consistent in density, and can be printed with little or no changes in the darkroom. I expect this would be true also for scanning the negs...
JLW makes some very good points. The bottom line is, in my view, that there's no need for the meter in a Leica M6, and you willl not miss its absense in an M2/3/4. The M7, with its AE feature, is a different matter.
