One of the bugging issue with iPhone that I found recently is that "other" space is getting bigger and eat up all space in iPhone. It started causing sync issue of Music category.
After short search I realized that many has the same issue with me.
General solution from Apple is like this:
http://support.apple.com/kb/TS1503
But, my case is different from any of above. In my case, thousands of voice recording files was having been self-increasing. Lucky to find this. After deleting those files using iPhone Explore application, the issue solved.
Hope apple will get back previous quality.