Take a look at what I read here:
WPA-based encryption, or Wi-Fi Protected Access, is similar in theory to WEP but doesn’t use a static network key, but rather a “Temporal Key Integrity Protocol (TKIP),” which changes keys with every data packet sent or received. This by itself makes WPA a very secure method for wireless networks, but the problem is that in most home-based environments, a “shared pass phrase” is used to access the network. If this pass phrase is any word found in the dictionary, a hacker can crack it through what is known as a “brute force dictionary attack.” While it may take a long time, it can be done.
A longer explanation is given here How WPA wireless networks are hacked, and how to protect yourself - February 7, 2009
According to the above explanation, one way to defeat my key will be to use brute force dictionary attack, but my key which is about 15 characters long and randomly selected characters will be kind of hard to crack with a "brute force dictionary attack" unless there are other methods, which I don't know.
I think I should not be so paranoid about the security of my little intranet at home. The article goes on saying that there is a WPA (RADIUS) version which is more secure than the one I use, but I don't think my router has the RADIUS version available. Even if it were available, I am sure that most of my devices will not be able to get wireless connection using the RADIUS version of WPA.