Keyword stuffing, yay, or nay? (how about concatenation?)

Question 1: Keyword Stuffing:
So I don't personally stuff too many keywords into my Meta's, I usually set the limit at 14. I try not to overdo it in my title either.

I do notice a lot of people stuffing 50+ keywords into their METAs and an endless trail of keywords into their title. Does Google penalize for this?

I've heard many-a-time that it is bad practice, but never seen an adequate explanation.

My educated guess: stuffing too many keywords means Google will pick only several of these keywords to actually use, and you'll have no control over the ones it picks.

Again, that's purely speculative. Can anyone elaborate for me?

Question 2: Keyword Concatenation

I've noticed that instead of using full keyphrases, some people break them apart.

Consider an optimized website that (physically) retails Apple accessories in New York:

-A- keywords =
mac accessories, apple accessories, macbook accessories, macintosh accessories, vintage macintosh, macintosh parts, new york city, brooklyn, bronx, nyc, manhattan

VS.

-B- keywords =
mac accessories nyc, apple accessories nyc, macbook accessories nyc, macintosh accessories nyc, vintage macintosh nyc, macintosh parts nyc, mac accessories brooklyn, mac accessories manhattan

See the difference I'm trying to point out?
I always do -B-, but I notice -A- is extremely prevalent.

Of course your specific keyword research is important, but I've seen google rank sites using -A- very well before! Does google consider keyword combinations as well as all the concatenated key-phrases I'm coming up with?

Real example:
Consider this Google search: cooker repair essex.

First result down, keywords:
<meta name="keywords" content="cooker, repairs, oven, fan oven not heating, gas, electric, london, kent, middlesex, surrey, sussex, essex, oven repairs">
(I realize that they have these words in the title too, but I see this happens often)