Very low Keyword density is ONE of the keys with MSN. (Low rank Penalty)
Repeat each KW no more than twice in description Meta Tags and no more than 3% overall page KW density. Also likes KW's in domain and page names.
Of course other factors might be at play...Link Farms, irrevelant link backs, etc, etc...
If you have good traffic from G...I would'nt touch a thing.
I might add that Y likes low KW density also.
We have good traffic from MSN and Y, but few from G.
If your G traffic is not that great, you might consider optz for the others...we did and we are happy.
I don't bother with G any longer since the big bust that put so many people out of business. Of course, if G was my big traffic generator,
I'd probably be singing a different tune. :-)
Good luck, Fish Texas