This is a rather broad question, and it seems like you're seeking advice rather than a strictly halachic perspective.
In general, if the microwave will definitely be used by only Jews and only kosher food is placed in it and it is designated as being only dairy or only meat, then, there shouldn't be a problem. The main reason that I state "only Jews" is that there could be a problem of "Bishul Akum" even if a non-Jew places kosher food in it, or even a potato.
Practically, though, I wouldn't recommend this in a mixed environment. Most workers, I find, are both careless and "care less". Non-kosher food will likely get into the microwave accidentally or even purposefully. There are loads of Gentile and Jewish anti-Semites who want to cause a problem, and this is an easy way to demonstrate it, and no one will know the difference. After all, when you're not there to observe, they've cooked their food in your oven and eaten it, already. Essentially, it's highly unlikely that anyone there will guarantee that the microwave stays kosher unless a reliable Jew is standing guard watching everything that enters it.
Case in point - someone I know works at Price Waterhouse. He says that on his floor, about 80% of the people are yarmulke / hat and / or "tzitzit-swinging" Jews. Despite that overwhelming majority, they won't put a kosher microwave in their pantry mainly for the reasons I mentioned, as well as that even among religious Jews, no two people have the same kashrut level.