WEP encryption is extremely weak and can be broken EXTREMELY easily.
WPA, not so much.
Any truly sensitive information such as a financial transaction SHOULD be carried out in a specific manner that makes it very difficult to crack.
SSL for example, from the Symantec website:
What Happens When a Browser Encounters SSL
1:A browser attempts to connect to a website secured with SSL.
2:The browser requests that the web server identify itself.
3:The server sends the browser a copy of its SSL Certificate.
4:The browser checks whether it trusts the SSL Certificate. If so, it sends a message to the server.
5:The server sends back a digitally signed acknowledgement to start an SSL encrypted session.
6:Encrypted data is shared between the browser and the server.
as long as the data is sent in a secure fashion, people can sniff all the packets they want, but without the relevant encryption keys they cant get access to the information held within.