I suppose the 1st thing to point out is that the internet isn't the big money spinner that it was during the initial .com boom. 9 times out of 10 if you research things properly you will find that someone out there is doing the same if not something very similar to your business or your idea.
That doesn't mean that you shouldn't want to develop and move forward with your idea, but it does mean that if you do you need to do lots of research, find all of the competitors, and find out what you can do better than them. The current trend with web design and development seems to be that most businesses have had a website of some sort, some have had good experiences, some have had bad...very bad, either way, everyone is moving forward and looking to develop their web presence for a more professional and/or functional end result. Often you will find certain sectors that have tired, homemade websites which are the leaders in the market, whilst these competitors may have a head start they won't deliver the same experience or image as the professionally designed website you are thinking of setting up.
My main message here is that no matter what type of E-Business you are thinking of setting up, ensure you do lots of research. The better understanding that you have of your target audience and competition on the web, the better chance you have of taking a slice of the pie and making some decent money.