My short answer is No!
I for one do not assign an encryption key to my wireless router (they're easily crackable anyway), instead monitor the router and if I feel someone is abusing I block their computer's MAC address. Because I believe sharing works! Specially when telecom companies charge unreasonably high amount for WiFi access, not to mention the fact that they usually charge by the hour (say you want to check your email for 5 minutes, then you've got to pay the cost of 1 hour access which is around $8).
There have been so many situations where I needed wireless internet access to do something small yet urgent. In fact this very post is brought to you by my neighbor's wireless since my DSL connection is down (read my previous post)! It is very crucial for me to check my email for voice-mails (I switched to VoIP so my home phone is also down) and job-related emails. If it wasn't because of my neighbor's WiFi, I would have committed suicide by now. A few months ago I was in Vienna for 5 days and I used a neighbor's WiFi to do the usual stuff and send a back-up of my pictures to my server in Canada.
If using other people's wireless internet helps me so much why not let them use mine too? A "piggy-backer" using the usual stuff like email is not a concern for your bandwidth usage, even for someone with a heavy load (take myself: 5 computers one of which is an always on web server and now my VoIP gateway uses the same DSL line for phone calls) and I bet most people don't even use %10 of their band-width (got get some statistics on that) so why not share?
If we all shared our WiFi then we'd all have free WiFi access anywhere. Just like file-sharing except no one's getting hurt here.
There is downside however. Even though someone who is using your internet once is most probably not going to abuse your bandwidth, there can be other potential risks of abuse. For example they can use your Internet access to do something illegal anonymously (to be more precise, under your IP address). But - last time I checked - in Canada the law the wouldn't allow telecom companies to disclose your information, so at worst case you might need some explaining for the telecom company (to stop them from canceling your server for abuse).
With the new WiMAX technology with much larger range, we don't need to be near a router and we can take our high speed connection on go. WiMAX is like cellular network for high speed internet. It is already being used in some areas and will be in the general market very soon (in a few months). In fact in theory (that is in a real world without corporate pressure) municipal governments could provide WiMAX for free and in fact some have already planed this. WiMAX is meant to work with WiFi not to replace it, nevertheless, probably in a few months no one's going to talk about stealing WiFi anyway.
This article on CNN.com includes a few comments from lawyers about the legal matters of WiFi access in the US and it is what encouraged me to wire this. Otherwise I'd just wait for WiFi :-)