WiFi and Personal VPN
If you're going to use WiFi, you should consider using a personal VPN to protect yourself. It encrypts your data so anyone intercepting the signal can't read it.
I use the following one, but there are several. At least look at what it does for you if you're not already using one:
http://www.witopia.net/welcome.php
For email and internet browsing the overhead and extra hop to the VPN server isn't too noticeable. It is noticeable on streaming video.
Claro - 3G wireless internet without signing up for a plan
If you want to use your laptop in places that do not have internet WiFi or cable, look at using Claro 3G. You can purchase the mini-modem for about $199.00 pesos (about US $52.00) and buy top up Claro cards and use the internet anywhere you can use a Claro phone. It costs about 3 pesos per hour. My experience is about 1.6Mbits/sec down and 0.12Mbits/sec upload sitting in my apartment in Recoleta. I use
http://speedtest.net/ to measure the speed.
It took several trips to Claro before I could use it reliably. I think more to my misunderstanding Spanish and the procedures, than due to Claro. If you try this approach and need help in English, let me know. I don't know a lot, but I can now use it consistently.