I haven't trimmed the stem of mine at all because it's not a bother to me, but I know some of the women at the the menstrual_cups community on LJ have completely removed their stems with no negative side-effects. I guess it all depends on how easily you can get a grip on the bottom of the cup.
One of the women strongly suggests a bevel edge. I don't trust myself with an exacto knife enough to try, but she swears that it's much more comfortable.
glapaloopscap's illustration:
I've also found that the 'figure 4' method of insertion, where it's sort of punched down into a '4' shape is much more effective and comfortable for me when inserting. The
memories section is a pretty good place to start accessing specific information.