First off thank you for writing the article. It doesn't seem to me that Facebook or Google saw a huge market inflection and decided to create a company in the hopes if hitting it at the write time. To me it seems they were doing something PG mentioned which is building something they themselves wanted regardless of the market potential. It just so happens that by doing this they built something that a lot of other people also wanted and were able to execute it in such a way. Sometimes I feel "looking for an idea" is the wrong approach but instead viewing the world from behind a critical lens we will see problems that need to be solved. By solving them we feel our lives will be better and maybe that is enough to begin with and by solving these types of problems, once in a while we may just discover that others feel the same way.
I had this idea when I received emails with attachments on my phone and wanted to save them. Let me know your thoughts and if you think it could be monetized.
I would go for iPhone. Mostly because the tooling is easier, interface builder is cleaner. Android is great too but a litle more involved to get the same result. At least that is my 2 cents.
I created an app called Scan4Points which uses your barcode scanner to get nutritional information and calculate the WeightWatchers points. Actually my wife had "forced" me to make it. She said it was finally something I made that she could actually use. http://confered.com/apps/Ryb70