Rationalism should not be confused with rationality, nor with rationalization.
-Wikipedia article on rationalism
I frequently see people using rationalism in place of rationality. Usually other commenters understand them, however I believe that using the word rationality is superior. The Less Wrong tag line is "A community blog devoted to refining the art of human rationality". On the other hand, rationalism is the philosophical term for a very different epistemological position. Furthermore, -the -ism suffix has some undesirable connotations.
We use rationality and rationalist, the latter with a more or less specific meaning not used outside these circles. It's not a big leap to derive rationalism in the corresponding sense (i.e. the attitude of striving for improved rationality) from rationalist. I don't think this would be a huge problem, least of all internally. It's not like there's a big danger of mistaking anyone here for a rationalist in the traditional philosophical sense.