Asking a new employee from an 'ethnic minority' if he or she is the new cleaner is bad because being a cleaner is not perceived to be a 'good' job.
Asking a new female employee if she's a designer isn't so bad because, as far as I can tell, being a designer is no 'worse' than being a programmer.
Both examples could be considered something-ism, but I'd say the former is worth caring about, and the latter is a case of oversensitivity (potentially from both sides).
I generally try to err on the side of caution to keep from offending people, but I'm quite allergic to people that get offended too quickly.
(A special place in hell is reserved for people who get offended on behalf of other people.)