I get to hear a lot of ideas from people wanting to start a company. The vast majority of the time, people want to start a “sexy” business. Whether that be the current hot online trend (at least half of the ideas I hear related to the web involve some sort of social networking) or even something more simple like starting a bar.
The problem with sexy businesses is that a lot of people are going after them because simply as a result of them being sexy or exciting. But those businesses are generally highly competitive as a result of the vast number of people going after them because of their appeal.
If you are trying to start an online business similar to what 1,000 other people are doing, you need to have a something remarkable or meet a demand no one else is meeting, which is more likely going to be a specific niche.
People also generally go after the sexy business ideas because that is what they hear about in the media. They hear about valuations and acquisitions of these companies that seem exciting. But I see many, many hundreds of million dollar deals with companies no one ever hears of and many times it is because the business is not exciting/sexy.
Look for that path less traveled.