As Jason suggests, you should try to find the answer to your questions in your own frustrations. Where there is frustration, there is a market (usually).

I went through the exercise myself and blogged the results: http://aymeric.gaurat.net/index.php/2010/my-frustrations/

I would love to hear people's frustrations too.

Agree with Jason .. scratch an itch .. that way, even if nothing worked out, you would still have one loyal user -> You

In good probability, there'll be others who share the same itch.

http://www.paulgraham.com/organic.html

I always find it hard to organize my reading (for most part technical reading). Do you think a service can help there? Like I can keep a track of books and papers I want to read and also get ideas from other people based on what I am currently reading/learning.

amazon.com, shelfari.com, anobii.com?

I am thinking more like a site that can help you stay focused and also provide motivation (by hooking you up with real people who are learning/learned what you are learning right now).

So yes .. its like shelfari but more focused on learning than casual reading

or try contributing to an opensource project that interests you