I'm using the CRM for Outlook Client, and get an important e-mail from prospect letting me know that she's going to check with her top sales people and get back to me with a couple of dates for a meeting.  I select the e-mail and click on the "Track in CRM" button. 

A day or two later, I'm reviewing the activity history of this company in CRM and I don't see the e-mail that I know I received.  So, I go back to Outlook and find the e-mail in question, I note that it is being tracked in CRM, so I select it and click the "View in CRM" button.  I notice that the e-mail address is highlighted in red which means that it did not resolve to an existing CRM record (be it an Account, a Contact, or a Lead).  I checked the contact record and saw that the e-mail address is, in fact, correct.  So why didn't it resolve?

I recall reading about this on another blog a day-or-two ago, and the exact scenario just happened to me.  What happened was that the CRM Account / Contact records were created from a Lead that had an e-mail address.  Both Account and Contact were created with the same e-mail.  Thus, the e-mail activity does not know which to resolve to: the Account or the Contact.  The way to solve this immediately is to delete the e-mail address from the CRM Account record (the company).  To solve the problem going forward, so that it doesn't happen again, I change the mapping from Lead-to-Account so that the e-mail address is not automatically populated in the CRM Account (company) record when the Lead is qualified.  E-mails are most appropriate at the Contact level anyway, so this makes good sense.  Just one of those little things that makes this powerful CRM system more user-friendly.