I know many people have moved to Gmail as their primary email client.  I've stuck with Outlook because it integrates with other systems, my pda and such.  Many people are not satisfied with Outlook because of the SPAM filtering.  I've found one product very helpful, Cloudmark.  It is unique because over 2,000,000 people contribute to what email is considered spam.  This brilliant way of handling spam means when people mark a message as spam, your inbox is automatically protected.  Or as they say it:

Only Cloudmark has the power to apply human feedback in real time to block spam, phishing, and additionally many viruses and spyware. Leveraging a highly sophisticated Trust Evaluation System™ (TeS) and groundbreaking technology, feedback is corroborated in real time, so that only a few people ever have to see a spam email before it is blocked for everyone. Cloudmark Desktop is entirely transparent and requires no configuration, making it powerful, yet simple and easy to use.

Try a FREE trial of Cloudmark.