Working on an open source Project that I hate...

I hate to say so but welcome to the real world. You can't always expect to work on cool and hip projects using the latest tech. There will always be "boring" clients with real world problems that need to be solved. It's all about what YOU make of it.

Often the little things make an assignment challenging. If it's not the client or the problem itself you should be looking in another direction. Perhaps you can practice on your soft skills and get your co-workers motivated. Building a motivated kick ass team is a real challenge and will gain you useful experience.