Jon Udell has referenced a solution for providing simple single sign on. Its so elegant and simple I have to wonder why I didn't think of that. If you use the same password for multiple web sites and think this is risky I recommend looking at this. From a security perspective this is a no-no. Though as Bruce Schneier has stated
"It's an old story: users disable a security measure because it's annoying, allowing an attacker to bypass the measure."Having to think of different passwords for different sites is annoying so we don't.