I run a company that has been creating site builder products for 6 years now (sitezoogle.com). It is one of the toughest markets for a web app, in my opinion.

I run a company that has been creating site builder products for 6 years now (sitezoogle.com). It is one of the toughest markets for a web app, in my opinion. On the dev side, there are very high requirements for each market. Take Realtors. You'd need to interface with MLS -- problem is each MLS has different requirements, and there are dozens in the US and Canada. Some have XML feeds, some only let you use an iFrame, others let you only download listings via FTP (!). You'd also need an internal CRM to help agents manage visitors and market to them. Both of these functions take a lot of dev. Then there is the competition. Take realtors again, and do a search in Google. There are hundreds of competitors, and therefore the adwords PPC is in the $3 range for the top listings. We've succeeded (profitable since 2004, 10 employees) by focusing on underserved niches (Landscapers, Horse breeders) and working closely with them to understand their needs. But, it is definitely NOT easy to go across dozens of market and have a compelling product and market it effectively. We are looking for help, so if anyone is interested in this market, send me a msg!