If it were to be built, what is something that'd you pay for?
In the spirit of helping others come up with project ideas, and then having a need be filled, mention anything that you'd find useful during work, etc.
I would pay for 'kid-safe springboard' for iPhone. Basically something that lets me quickly switch to a 'kid mode' where only apps that I want my 5 year old to play with are available, and maybe even disable Internet to those apps. Sometimes you just don't have their device(s) handy when you'd like to occupy them, and you don't want little one replying-to-all in email... That would be acceptable also -- lock-out of certain apps/groups. And for regular, not-jailbroken iPhones. I do realize this probably isn't possible given what Apple lets you officially access. But maybe there is something creative possible?
i think this would only work if all the apps you need can be contained in one app and you have a certain kind of ipad cas/sleeve that physically locks the home button.
I'd pay for a "Kindle highlights & notes, for groups." I very often have the "everyone in my team must read this book" impulse, buy a bunch of copies, and then it's really hard to sync who's where, what they're finding interesting and to share notes.
The notes you take for yourself aren't the same ones you'd take for/with your team (imagine highlighting something and saying "see @jack, this has everything to do with what we were discussing on that project", it'd be awesome).
The last few times I've bought glasses, I was unhappy with my choice within a few months. I'm really lousy at judging what looks good on my face, and the sales staff aren't much better.
I'm envisioning a mobile app that lets users submit two pictures of them wearing eyeglass pair #1 and eyeglass pair #2. A user would have to vote on X (5?) other users before their submission would be open for voting. It would probably need to be ad supported.
The only things different than what you asked for are 1) people aren't directly comparing one photo with the other and 2) the people doing the judging are looking at you with under the lens of dating (which I think would be okay in this use case.)
Also, saying that it would probably need to be "ad supported" suggests that you might not be willing to pay for it, though.
A device for electronic-hacking that allows me to use screens removed from Nintendo DS or Playstation Portable or some smart phones (probably iPhone because of ease of getting them) over USB. A bit like (http://www.thinkgeek.com/computing/usb-gadgets/bfa3/) but not insanely expensive.
There are very many dead laptops with working displays. Something that allows people to use those as a secondary display (even though they're going to have to work to rip out the display and stick it into a case / bezel) would be good.
Device would consist of a really nice handle. This would have a socket for an attachment. There would be many attachments available. Each attachment would take one type of razor blade. Thus, the buyer would buy one nice handle, and a couple of attachments (for each blade type that they like).
The user sends in a knitting pattern; the website generates a cost; the user decides to pay (or not); payment is taken; the thing is made and dispatched.
Advanced mode: have a screen for users to design stuff which then gets knitted.
Printable solar panels, fast and cheap DNA/RNA sequencing, teleportation, space elevator.
If you're talking about software, a true photoshop alternative (not GIMP) would be cool, a cheap Splunk alternative (their licenses are insanely expensive for large sites).
