I guess your question depends on what your doing when you ask if WiFi is safe. 

Surfing sites that use HTTPS with a decent level of encryption would definitely be safer than surfing standard websites where everything is sent in clear text.  It's also important to verify that you are not first logging into a non-secure site that only becomes secure after you log into it as you run the risk of your personal information being compromised by an identity thief.  Reading the news or checking stock prices for example is safe...but be careful when doing social networking, banking or online transactions. 

Be sure your always on a secure (https) site if you must do those things on WiFi.