Print Ads, Commercials, Placements on TV. Radio spots. That is when people want to see/hear example.com and not example.net and even then I doubt too many would be turned off on the .net point alone.
If you are soley promoting your site through SE then I wouldn't be too concerned about it. It is rare that people read much more then the Title and Description of sites in the search results page. Some will glance at the TLD but I don't think they will be turned off by the .net
The major thing is if your content is better then the .com guy.... IMO
Out SEO him and be more relevent and one day you might be able to make the .com guy an offer for his domain.