It's a huge marketplace online and opens many doors. But it is fraught with pitfalls and because of the hundreds of millions of "voices" all screaming for attention, it is difficult to get noticed amongst the crowd. The most successful businesses are those that have a ready target market and can get information from their existing customers about what they want the website to do.
In my case, I have created the adgreement.com website from nothing and with a business plan based only on titbits of information put together as the project gathered momentum. It's not planned like previous businesses and I will have to see where it leads. I have had an online retail business, which did really well for just over 2 years but was too heavily reliant upon *Bay for sales (I don't even want to mention their name as they don't deserve a mention, but you know who they are!)
The fact is that it remains extremely difficult for start-ups to get noticed online. Unless you have enormous marketing budgets or someone skilled enough to produce a mass-marketing campaign to drive traffic, you are stuck in a limbo trying to start off from scratch with limited resources. The days of businesses starting off from nothing are evaporating, because you need a huge resource pool to raise awareness and build a brand in a short time frame.