I can add the tool to my custom toolbars, but the next time I open a new ArcMap document, the custom toolbars are there, but the tools are missing. The only way that I've been able to keep the python script tools on my toolbars is to save to the mxd. I would like to have them available always, not just when I open that particular mxd. (I'm using Windows XP, ArcGIS 10.0 SP3)