WR> LED's come in all sorts of voltage ratings, with different 
 WR> current ratings too. 
Eh?  Most of what I've seen is spec'd in the 1.6 - 1.8 volt range,  with the 
exception of the stuff that's designed with a built-in current limiter,  but 
that's not the same thing at all.
 WR> If wired in series (N of one hooked to P of the next, and so 
 WR> on) 3 volt LED's can have four across a 12 volt circuit. 
Where do you find 3 volt LEDs?  And what's going to limit the current in that 
setup?  Have you ever seen the voltage vs. current curve of one of those 
parts?  It's damn near a vertical line!
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