The problem with Diigo is caused by the security feature of IE7 that reduces the number of ActiveX controls enabled by default. this means, if you do use Diigo, you will likely get repeated message bars at the top of the screen preventing access until you click on the bar and allow access.

There are a couple of ways around this. you can then go in to the Security Settings in Internet Options and “allow previously unused ActiveX controls to run without prompt”. this will however allow any other ActiveX controls to run without intervention. there are more complicated ways to run just one application such as adding the control to the pre-approved list in the registry. this requires manual changes to the registry. You can find details about how to achieve this here