How big should the logo be on my website?

Without a doubt, an interesting array of logos. Certainly we can all draw our own conclusions.; but what are yours? I would be genuinely interested to know how you, as a fellow design professional, view the use of logo design on the web and communicate this to clients. Certainly, clients always expect their logo to dominate the design but explaining to them that the logos of major brands are often a third of the size meets with blank stares. We would all like to think that the answer lies in client education. The problem is that clients don't come to be educated, they come to have their problems solved.