Penalized for too many keywords?

Will you get penalized in the serps for using too many keywords? If so, how many is ideal? If not, why don't use 1000s of meta tags?(shit, maybe they do?)

i doubt its any use these days even if you use billion meta tags. But if you want to target for many keywords have them in your content.

Go for 2.5 to 5 % Keyword Density and you should be fine.

Yes, you will get penalized. Big G will ignore your meta tags.
I don't remember maximum amount of keywords you should use but something like 10 should do fine.

Do you mean too many keywords in the meta keywords?

If so I think 4 is a good number. In terms of keyword density, general advice seems to be between 3%-5% visible, and upto 8% overall.

There is no limit that is set for Meta keywords limits. There are several search engines that have their own limitations as far as keywords are concerned.So then you may be faced with separate keyword limitations for different search engines.Here are links that will help you ascertain your keyword limit.
webmasterworld
daniweb

Unlike Title and Description Tag, there is no pre-specified word limit for keyword tag. However, all major search engines including Google now ignore meta keyword tag completely. To test this, you may remove all of the keywords in your meta keyword tag and after a week or so your ranking will not be affected at all.

Similarly, adding hundreds or thousands of keywords would not make any difference, but will end up increasing the load-time of your pages. Page load factor however is indeed one of Google's ranking algorithm factor. So, keyword stuffing in meta can indirectly end up hurting your SERP than improving it.

meta keywords just do not work anymore!