Lets look at the first step in the list: "Postulate":

1. Postulate - Take a guess what the market wants.
2. Simulate - Don't write the full functionality yet. Write a skeleton that emulates the product.
3. Demostrate - Show some potential customers and some non-potential customers and get their feedback.
4. Integrate (feedback) - Filter what comments are good and change your simulation.
5. Iterate - Go back to step 1 or step 3 and do it all over again.

Guessing what the market wants based on trends in the news, trade periodicals, and market studies are one way to postulate a new Web Service.

But, sometimes it's just a question of what would make sense as a product or service in your own daily life. I came up with these items for a possible Web Service:

1. Locator service of family members - Where's dad? Where's mom? Where are the kids? (Maybe GPS co-ordinates or a map with icons)
2. Price/info lookup service - You give a Bar Code # and you get back the price and product info.
3. Parking service - Give GPS co-ordinates or zip code and get empty parking spaces or available parking lots in your immediate area.
4. Stock price service - Self-explanatory.
5. News service - Get the latest headlines.

I listed the above in descending order of preference. But, jumping to step #3, I'd like to get some feedback. Post a comment to vote for one of the other items (other than "Locator service of family members") from my list above or add your own item.

I'll gather some feedback and pick which Web Service I'll use for this exercise.