When I worked at medium-to-large companies, I used to dread the yearly "performance self-assessments". Not that I didn't want a raise, but writing about my own performance was agonizing. It reminded me of writing college entrance essays, another torturous process for me.
But at some point, I figured out the key to a quick and easy self-assessment. Think of how promotions work: My manager goes to a meeting of his peers, led by their manager, and they go around the room and make a case for promoting each of their employees. I just need to make sure that my manager mentions all of the good stuff I did that year.
For my next self-assessment, I wrote up a short bulleted list, one sentence each of every thing I wanted my manager to say in that meeting. That's it--it was shorter than this blog entry. This approach may not work for every company or manager, but my manager at the time told me it was exactly what he wanted.