I presume it's uncontroversial to say that it would be useful to have terminologies available as web services. Right now, you can browse various sources of reference terms that are useful to museums (amongst others): sources like the british & irish archaeological bibliography (including its approved term lists); the National Monument Record Thesauri; and the museum codes and SPECTRUM terminology termbank maintained by the Collections Trust (to highlight some UK examples). I'm certain it would be useful to have these available as web services (some more so than others); likewise other thesauri that AFAIK aren't available to programme to: ULAN and AAT, for example, which are collected under the CCO initiative.
There's every chance that I misunderstand some or all of these "services" in terms of how they're used and by whom (I'm very shaky on the status of CCO and its relationship to AAT, for a start). But I'm sure that there are many ways in which a programmatic interface to their contents could be used. Which is why (to get to the point of this post) the service that OCLC's top geeks have come up with here is a great example for us in the museum world to look at (blogged here on Hanging Together). This is a collection of esssentially library-related thesauri onto which they have created web services. I like the look of FAST best of all; it could be really useful for us in the dusty bones world too.
Lorcan Dempsey also blogs today about the WorldCat identities API and other cool services. I fancy the name look-up service: aside from anything else it gives us a URL to refer to for those individuals in the WorldCat database. Here's a not-so-random entry.
So once again we can learn a lot from libraries leading the way. One of the cool things, though, is that OCLC are a cross-domain organisation, and people like Dempsey think constantly about breaking down the barriers between libraries, archives and museums. If they've sprinkled their magic onto library terminologies, I'm sure they'll be only too happy to help the museum world to take similar steps.