Separates vs. Integrated

With so many good integrated amps out there (Cary, Conrad Johnson, Musical Fidelity, etc.), what are the real advantages of going to separates? It seems to me that there many folks who simply assume a first-rate system includes a separate preamp/amp set up. MY ACTUAL QUESTION: What has been the experience of those who switched from an integrated amp to a separate preamp/power amp set up? Assuming that the extra money was spent, was it worth it? Thanks!