The Comodo SSL hack last month has shown quite dramatically that SSL is prone to man-in-the-middle attack if you live or use SSL protected websites and services in places that make it easy for attackers to spy-on and divert IP packets. The way the attack works is that the data traffic to an SSL protected site is redirected to another server that then poses as the original server by sending a fraudulent SSL certificate. Out of the box, web browsers today don't indicate this to the user if the fraudulent SSL certificate was issued by a trusted but compromised certificate authority. For the technical details, see the excellent article on Ars Technica.
So is there anything that can be done to protect yourself against it? Two things come to mind:
First, whenever in a non trusted part of the Internet, a VPN tunnel can be established to an endpoint that lies somewhere where a man-in-the-middle has no access to. Many VPNs use certificates, too but since they don't rely on certificate authorities, man-in-the-middle attacks with bogous certificates won't work. The only solution for an attacker is to block VPNs from being established, and that the user notices immediately.
The second way to detect against potential fraudulent SSL certificates is to be informed if a different certificate is presented to the web browser for a website than at a previous visit to the same site. There are valid reasons for this such as the old certificate being close to its expiry date but such certificate changes are very rate. The issue here is that web browsers do not show such a certificate change. For Firefox, however, there are add-ons that do just this. An easy and straight forward one is Certificate Patrol.
The problem with both solutions is that the ordinary user without a technical background is unlikely to use either one.
On mobile platforms, using a VPN is not quite as straight forward, as keep-alive packets will drain the battery very quickly. Let's at least hope Firefox mobile and other mobile browsers get a similar add-on soon. However, that still leaves data transfers vulnerable from other apps such as email programs that use SSL to potect SMTP, POP3 and IMAP connections as well as apps that use HTTPS for data exchange.
I agree with Ars Technica, the security architecture of the Internet needs a serious overhaul.