I'm working on a new venture with a friend of mine, and we set to meet as many potential customers as possible before writing even a single line of code.
We've met with 2 customers and both of them really loved the idea. Is it enough for moving on to implementation or should we meet other possible cusomters?
I heard a horror story the other day, where an individual got raving reviews from every customer he spoke with. After they launched, not a single one cared to use his product. Cost him a small fortune.
What you need to start doing is getting commitments from individuals. Just like area 51 stack exchange is doing. Just get 200 people that are willing to commit to your idea if you go live with it. This is of course if you've got something that's going to take a considerable amount of time or money.
Otherwise, if you can, get a prototype out asap and start showing it to clients. Again, to get commitments from them.
I recommend “Four Steps to the Epiphany” by Steven Gary Blank. This book teaches you how to talk with customers through your entire development process and adjust continually.
AS Jontahon pointed out, market research does not tell you whether your customers will actually use the product - it simply tells you whether they like the idea of it.
This is called Attitudinal liking - your attitude towards some product is positive, but when it comes to opening up your wallet you might decide otherwise. For example, lot's of people admire Macs, but purchase PC's.
Therefore, there is no other way to test the product other than actually launch it and see how it goes. The wisdom is to find a way to invest as little time and money to launch a functional product you can test, then build on the feedback you get.
Before that, make sure you understand the market you are entering, which means you can answer YES to following questions:
1) Does your product solve a specific customer problem or issue? (product benefit)
2) Are there enough customers who have this issue? (market size)
3) Are customers unhappy with current solutions or solutions do not exist at all? (competition)
Hope this helps.
Perhaps you could consider starting such a project via a site like http://www.kickstarter.com/ where people actually pledge real money to get a product going. You would then be measuring people's actual buying behavior, rather than simply trusting what they're telling you.
In addition to asking customers if they like your idea or if they would buy it, also ask why they would buy it and how they would use it.
If they have time see if you could associate prices with features and get some idea of how much extra they would pay for features that you think are important (and are difficult or cheap to roll out).
If you can document the exact pain that your product addresses as well as the product features that are most important to your customer you can build a road map for yourself. You can avoid building difficult components that no one wants and focus on features that are relatively easy to roll out, well liked and better priced.
There is a world of difference in having a customer say this is a great idea and I would buy it versus if you could do a, b and c, I would be willing to pay 250 a month for it for the next 12 months.
When he says that you push for a close and a commitment.
I normally do it in reverse.
By that I mean spending a little time to get something up and running first. You will find that its a LOT easier to get people to commit when they can see something instead of just hearing about it.
It's rare to find a salesman who can talk his way into a "sale" with nothing in hand, much less a developer.
That plus if all you do is talk to consumers, you tend to end up with stuff that takes FOREVER to finish because you are:
Get something rough working, pitch it, sell it, then refine it. I believe doing it that way works out better in the long run.