I don't want to repeat past discussions, so here are some threads worth to read:
- Plural vs. Singular [webmasterworld.com]
Google's treament of plural vs. singular keywords
- Singular Vs. Plural - What do users search for. [webmasterworld.com]
Do users search for blue widget or blue widgets?
- Singular vs. Plural extrapolating from wordtracker [webmasterworld.com]
Is "widgets" better than "widget" ...?
- Words that could be two words [webmasterworld.com]
Logfiles and Log Files, Website and Web Site
- Finding the right keywords - Data Mining [webmasterworld.com]
Using the right sources to find the right words
More: Singular vs. Plural and related keyword discussions. [google.com]
And in case you're still interested in this topic, you will love the WebmasterWorld forum Keyword Discussion [webmasterworld.com].
Have a nice read. ;)
At one of my sites i established a section called widgetbreeders some years ago - due to my lack of english language skills i used the one-word-version for the url as well as for all link anchor texts. Two months later i noticed the misspelling. Too late - the page allready received that much referers from google that i would be a idiot to correct the misspelling. Still one of my best pages. :D