George Toft wrote:

 CISSP Wannabe asks: As I read the Electronic Communications
 Privacy Act of 1986, the intentional reception, recording,
 decoding, and decryption of wired and wireless electronic
 systems is illegal.  Therefore, typing snoop, tcpdump, or
 ethereal on a system (for purposes other than troubleshooting)
 is illegal.  Furthermore, it would appear that netstumbling
 and wardriving is also illegal.

 Can someone disprove me?
 Regards,
 George

I had not heard the term "netstumbling" before.
Here is a message purportedly from an FBI agent that says
there are several potential violations at least implied
in this activity:
 http://www.netstumbler.com/article.php?sid=391
Accompanying comments suggest some legitimate uses of
scanning for networks.

An ISP sysadmin (who described himself as "anal about
security") said recently that browsing outside your home
directory on an ISP system (e.g. in the /etc directory)
was definitely illegal.  He mentioned no specific law.

Vic