I know that pg is a strong advocate of having multiple cofounders and many other people have even stronger views on this. I also see the benefits of having multiple cofounders versus having a single founder, but I don't think the impact/differences are as stark as many people make it out to be.
http://news.ycombinator.com/item?id=77525 had some interesting stats on how single-founder companies have had more success than 2-founder or 3-founder companies (within a sample of 100 publicly traded comapnies)
Scobelizer's interview of the AdMobs founder (http://blogs.wsj.com/venturecapital/2009/11/09/the-wisdom-of-admobs-founder-omar-hamoui/)is one more data point of how "one guy with a laptop" can build a hugely successful company.Incidentally Sequoia funded the 1-man company without any dogmatic rules on the number of founders (or for that matter employees)