It wouldn't work in practice. There are no sharp lines between these categories, and we'd be misleading people, one way or the other, if we insisted on drawing them. It already bothers me that circumstances force us to draw a line between green and yellow, because we're probably discouraging some people who should instead be encouraged. It would be even worse if we tried to draw a line between yellow and red.
What might be useful are comments overall like "we received several applications for online invitation services but nothing seemed innovative or compelling enough to us" or "we received a handful of applications for doing x but, in our opinion, the mobile space is where we think that market is headed". I think you once mentioned that you get a ton of hotel/food review website ideas. You've also indicated that you think the email overload management is an area of YC's interest.
Doing this might help at least some of the applicants get some idea. Not everyone is covered by these comments and no one is forced to take your opinion for it but it just helps to get broad feedback.
PG seems like a nice guy and is doing something really cool with YC, but it's not his job to give people advice, beyond the people he picks for YC. Part of 'not giving people advice' probably includes statistics on what sorts of applications are 'hot' in a given time period, which might actually be fairly valuable information that they want to keep to themselves.
If you want advice on your app, post an 'Ask YC' thing here and usually, people will give you some pretty good feedback.
Wouldn't it be a bad move to do this if you are still in "stealth mode"? I have been thinking a lot about this especially after having not been accepted into YC. Half of me wants to know what people in the business think about my idea, and the other half wants to wait longer until closer to launch?
