I developed a webpart that is supporting different languages so I had to put resources.dll file in web application's bin directory to make my webpart work properly. Now I got option of putting that dll in GAC or 12 hive, but not sure which one is counted as best approach as I am pretty sure putting it in web application's bin directory isn't really best thing to do as then I might end up having duplicate resources for each web application.
See there are several things to consider - if your web-part is designed for all (maybe almost) web applications in the server farm, deploy it in GAC. But if you know that the web-part is developed for one particular application why bother putting it into GAC? rather put it in bin. You also have the option of embedded resource, though very uncommon but that's one option too.