I have some WCF services that I work in quite a bit, and ever since I enabled the project to automatically generate an XML documentation file (so I could use Sandcastle to build MSDN-style help files with it) ... I started getting really verbose warnings every time I built the project.  It would warn me about any publicly visible types or members that didn't have explicit XML comments associated with it.  Because those comments wouldn't be exposed to the WCF client that consumes the service anyway, my team doesn't add XML comments to every class and property (at least not the ones where the name makes the behavior completely obvious, so that a summary isn't needed).

Every time I did a build I would see a ton of warning that said something like "Missing XML comment for publicly visible type or member..."  So, I wanted to supress all of those warning, so I didn't have to wade through them to see other warnings that really did need to pay attention to.  In order to hide a particular warning, you have to figure out what the warning number is for the type of message you want to disable.  One easy way to quickly find that in VS 2008 is to simply right click on the warning and click on "Show Error Help":

The help file that pops up, will contain a heading like shown below ... which contains the error number or warning number that you need to know to supress that type of message (highlighted):

After you have the number, all you have to do is set the project's build to surpress that warning number.  To do that, just right click on the project in Solution Explorer, and select "Properties."  Then, under the "Build" tab, find the section for "Errors and warning" and add the warning number to the "Supress Warning" textbox like shown below:

Note: You can also decrease the overall warning level for the project, which will make VS less verbose about non-critical warnings ... but I personally think it is a better idea to leave it at 4 (the default) and explicitly filter warnings that are a problem.