domain names and google

[Sleep[Walker]]

1 hyphen is all right. 2 - under question. I won't recommend.

i expect there is a limit as 3 or 4 + would be seen as spamming keywords?

No, i think that spamming keywords is something like "teeniest-teens-teening.com".
For example, lets imagine that we have two identical sites greenguysboard.com and green-guy-and-jim.com. And there is no penalties for duplicate content.
I am 100% sure that the first domain name will be ranked higher that the second one. I admit that i have no idea why is happening such thing, but experience in SEO practice proves that.