To recognize and honor outstanding ACM members for their achievements in computer science and information technology and for their significant contributions to the mission of the ACM. The ACM Fellows serve as distinguished colleagues to whom the ACM and its members look for guidance and leadership as the world of information technology evolves.Since then over 500 fellows have been named including several theoretical computer scientists.
Last year ACM decided that they needed more grades and recently announced their first class of senior members and distinguished engineers, scientists and members. Only a couple of theorists made these lists.
Becoming an ACM Fellow or Distinguished Scientist doesn't make you a better researcher but it does give you a little more clout in the broader CS community. Also having large numbers of Fellows and Distinguished Scientists makes the theory community seem stronger as a whole. So if you know of someone worthy (and eligible) for Distinction or Fellow, go ahead and nominate them and help give your fellow scientists and the theory community the recognition they deserve.