I've not been an official member of wikipedia for long, but I have browsed for a while, and done small edits (usually Grammar and Link correction)

Most of what I do you will never notice. I redirect and merge where there are 2 or more pages on the same subject (for instance; merging Nick Ut and Huynh Cong Ut and making the former a redirect), alter links to lead to the correct page instead of disambiguation, and checking external links to make sure they are still relevant and not returning a 404. Ideally all of these edits should be transparent and the casual user will never notice they are there.

My opinion on editing is: An Article is complete not when there is nothing left to add, but when there is nothing left to take away.