Wow, hot topic! I don’t understand the affliction people have with Manual mode. Three of my bodies have only manual mode and a basic meter. To change ISO you wind out the film and drop in a different role. Digital rocks! Four metering modes, change ISO for every shot, a computer to work out the exposure (sometimes even dual cores!), TTL flash, exposure compensation, flash compensation, Program mode, Aperture Priority mode, histograms! A techie delight! Perhaps the “use only manual mode” crowd are artists?
I agree with KeyAndFill, digital bodies contain a lot of power and if all you are doing with manual mode is centring the meter, you might as well get out of manual mode because you are working too hard. Manual is great in a studio and other places with consistent light. If light is changing from shot to shot, Aperture and Shutter modes are your friends. If you are using on-camera flash, or you have an off-camera arrangement that communicates both ways, TTL flash and P mode can work extremely well.
I don’t know about other brands but in P mode, neither of my Canon bodies with a pop-up flash, pop it — you have to tell it you want the flash. If memory serves, the Nikons I had worked the same way.
Histograms are extremely useful, if you understand them. Far more useful than relying on the image playback. With a little practice you can match a histogram to the scene and decide if you got the exposure or not, with great accuracy. External meters are helpful but not always practical, some subjects are just too far away to use an incident meter, and with partial spot and spot meters built into the camera, external reflectance meters are not really necessary. The Flash feature in external meters is helpful for setting multiple strobes.
All the new tools are wonderful, but you have to understand them to get the best from them.