A Hitwise post digs into the behavior of searchers and sees whether they prefer searching in the singular or plural. Using the term "laptop" versus "laptops," it is clear that "laptops" is the winner in search. When investigating nine other terms, the following was discovered:
...[W]hile the results are not conclusive, it does seem that plural terms are better at sending traffic to retailers than singular terms. Two thirds of the products tested performed better as plurals, with technology products in particular skewing in favour of an added ‘s’.
Of course, as one member on Sphinn notices, this is specific to traffic, not necessarily conversions. However, it's a good first stop. Now can someone compile a report on the conversions? ;)
Forum discussion continues at Sphinn.