There is a very common mistake that I have seen being made concerning the implementation of popup-blocking software. It typically involves one running a third-party popup blocker like one that is part of an add-on toolbar like Google Toolbar in one of the recent crop of browsers like Microsoft Internet Explorer 7 that has integrated popup-control functionality.
The problem can lead to popups that are to be part of your Web experience, such as a transaction wizard, being blocked or, at worst, the browser program hanging or crashing frequently. This is due to competition between the different programs to manage the same site or pop-up screen.
To avoid this, make sure that you are running one popup blocker program only, whether the third-party program or the one that is integrated in your browser. Personally, I would prefer to use the one that is integrated in the browser because of it being tightly linked with the browser’s code, thus avoiding use of unnecessary system resources.