A my current client we have a rather elaborate domain setup and I think it might be better to set up a trust relationship so the client domain is able to reference users and resources on the vendor domain. This will make administration of users much easier as well as making server administration much easier for the vendor.
So my question is... Is it? Easier, I mean. Is it easier to set up a trust relationship between two domains compared to managing, say 50, user accounts in 2 places?
It really depends on how often you need to deal with this domain. Setting up your trust, getting the permissions the way you want etc. can be quite a big task initially and requires a good understanding of both yours and their domains, and what you want to be able to achieve at the end of it. That said, once its done it will make your life a lot easier in terms of user administration.
So, if your regularly having to deal with these problems then it is probably a good idea to expend the effort getting it setup, if its something you only have to deal with once a month or so, then maybe your time could be better spent elsewhere?
This also assumes you do trust the vendor your associating your domain with, that you want to give them the extra access to your domain that creating this trust will bring.