Do I Use Singular Or Plural
Keywords In My Pages?

Question - The keywords that I've chosen have been the ones with the highest Wordtracker demand, regardless of profitability. I've pretty much ignored keywords with a yahoo demand of under 500 so far.

Where plural and singular existed I've always chosen the highest Wordtracker demand, although you did mention to me that it can be good to do both because one is often easier to rank for that the other.

I look for the version (singular or plural) that has the least competition in Google and run with that. Is what I'm doing correct?

Answer - Yes, sometimes you'll find half the competition for one version over the other with an exact match search (which is what you want to test for) so go with the version (singular or plural) that's easier. The demand will likely be similar for both, but the supply won't.

Go with the easy one...