I am using a corporate network and access the internet via a web proxy.

Computers that you don't personally own, or do not fully control physical access to, should be considered inheirently untrustworthy. Even with SSL, any network or system admin could probably easily get physical access to any computer in the building and install a keystroke logger. That goes for Internet cafes, too. Putting your CC num into such a machine is reckless.

The security problems of wi-fi networks are well-established. This is one of the few areas where SSL is quite benificial.

I'm not saying SSL is completely useless, just that if we got rid of SSL completely, the security of the entire system wouldn't drop as dramatically as most people think.