My current employer has just issued the following note about using wi-fi. They tend to be a bit over cautious when it comes to protecting data, which is no bad thing I think.

HOTEL AND AIRPORT WIRELESS
HOW SECURE IS IT?
This has been in the Newspapers and Internet News recently. How can anyone walk away from a free wireless connection? By simply starting your laptop, you can associate to free wireless access points (Hot Spots) in hotels, airports, coffee shops, and bookstores; but who else is connecting?
XXXX travellers need to take steps to protect business information in their care while working outside the office. If connected to a wireless hot spot, corporate users need to be aware of their online activity and assume that information is accessible by anyone. Do you have confidential, proprietary information on your laptop? If you do, your transactions are vulnerable to theft. The guy in the coffee shop, airport, or hotel nearby may be eavesdropping on the wireless network gathering confidential corporate information.
Wireless local area networks (LAN) have inherent security risks. Knowing these threats and risks is half the battle; securing your laptop is the other.
Although many travellers may see free wireless as a way to save the organization money, in fact, it may provide unnecessary exposure to theft. Without a properly set wireless configuration, data sent over a wireless network is sent in clear text, including e-mail. Before connecting to any free wireless network, it is important to take the following steps:
1. Connect through a Virtual Private Network (VPN). VPN connections are an absolute must for corporate users. VPN client software is a must for corporate users. This encrypts data end-to-end, between the client device and the corporate server.
2. Install/configure a firewall.
3. Install/configure anti-virus software and maintain updated signature files.
4. Make sure all operating system patches and hot fixes are up to date.
Overall, it is important to remember that when using a free wireless connection, data is vulnerable. Users must take the necessary measures to protect XXXX information. If you suspect your laptop has been compromised, contact GBR XE Electronic Security.
HOME WIRELESS SECURITY
More people are installing Wireless Broadband at home. Costs are now reasonable and it allows a number of PC

Like I have said before, if someone wants to steal some information from your computer then they will do, the tools available quite freely nowadays are more than capable of exploiting any holes you may have on your system, and wireless networks just make it that little bit easier

I for one love using wireless, but never ever would I use it with sensitive information on my laptop.