On the average I receive from 50 to 200 e-mails in my corporate Inbox which I believe is not high number at all. Still despite of the techniques I use to keep my Inbox clean some e-mails need to be stored for reference for months in archive. As you might expect it is difficult to find required e-mails in archive although I try to keep them in logical structure. Right now I use Windows Desktop Search and this tool is really good in full-text search when you need to find single e-mail. It also has some basic capabilities in handling e-mail threads. But unfortunately nothing more.
A friend of mine told about Xobni. An Outlook plug-in which Bill Gates refers to as "the next generation of social networking". I hope to allocate time and give this tool a try as I see no way how my e-mail counts may drop.