As seen in the screenshot, it is quite the simple little widget with a refined look that fits in nicely in a screen full of Dashboard widgets. The focus on simplicity is welcome. It really doesn't need bookmarks or any kind of a history; copy URL, go to dashboard, paste, (((fill in the blank))).
The only problem is that the widget is effectively unusable. The (((fill in the blank))) is a bit painful right now.
As demonstrated in the screenshot, the widget is just too damned small. All but the simplest of username/password combinations overrun the boundaries of the widget. To compound the problem, neither the username nor the password is selectable -- you can't copy/paste the username or password. Given that, without a hack or manual labor, Dashboard widgets and a Safari window are never going to be on the screen at the same time, this also means you don't get to see the username/password as you type it into whatever was asking for it in the first place.
The widget's charter is rock solid. The graphic presentation is quite good. It just falls apart when it comes to usability.
Update: Rock Solid if you wanted it in a Dashboard or you want it isolated from the browser. But, as both Ben and Ian point out, there is a bugmenot bookmarklet that is a hell of a lot better than any Dashboard widget could be. Not as graphically wizzy, but integrated where you want it. I wasn't aware of said bookmarklet (I feel so oblivious).
Just drag this link -- [BugMeNot!] -- to your bookmarks bar.