Two days ago my host (a fairly well known host that I recommend to almost all my clients) changed the trust level on all their shared .NET 2.0 servers at the recommendation of Microsoft. Unfortunately, little warning was given and some sites broke because they were depending on Full Trust. I had two of those myself, not really sure what was causing the need for full trust.
After investigation, it appears that third party web control I was using on these sites require full trust and was causing my problems. Now that I figured that out, I contacted those third-party companies and unfortunately those controls do not work in partial trust, although one company at least put the request on the feature request list for a future version. Not much comfort for me at the moment however.
Fortunately, the dependence on these controls is minimal and in my case will take some minor work to work around. However, I know of some other sites that will not be as lucky. I can understand the security reasoning behind running in partial trust, but it is very hard to explain to a client why there site which worked fine in the morning, suddenly no longer works in the evening, seemingly for no better reason than the site host upgraded the security. Security of your site matters little if it is down. So needless to say, I have some work ahead of me to change the sites to work under partial trust. I also imagine we will see quite a few updates to 3rd party controls to run under partial trust if that is what Microsoft is recommending to hosts now.
One good thing that came from this, it put me in a position that I had to learn more about the different trust levels and what I can and can't do in each....something I perhaps took for granted in the past.