I hope I don't come across as negative here, but I hate lists like this. Peopel are always raining on each others' ideas "Oh, what, you're going to make a myspace clone? Bahahahaha." (facebook) "Oh, what, you're going to make a facebook clone? Bahahahaha." (twitter) "Oh, what, you're going to make another dating website? Bahahahaha." (Okcupid, plentyoffish) "Oh, what, you're going to make another social bookmarking w…
If you see your project as learning about tech, then awesome. But I think the OP was warning against those that see their projects as paths to riches with those ideas. There are certain startup ideas that are perennial tar pits with good reason. There's something specific about the problem area that everyone's banged their head against, and often times, it's not a tech problem.
It'd be worth your while to understand it first.