[thelist] [tip] Macromedia even forgets (encoding user input)

[Sarah]

>Don't feel so bad... even the big boys forget.
>
>Open up macromedia.com and search on the following using the box in the
>top-right corner:
><meta http-equiv="Refresh" content="0;url=http://www.intel.com">
>
>Ooops.

I've had this message sitting in my inbox for a while, and every once in a 
while I think about it. But I am having a hard time figuring out a really 
bad thing that could happen as a result of not encoding user input. I know 
I used to do a lot of error checking on variables coming from the 
querystring until I decided that, if someone really wants to be a jerk and 
break my site by putting some garbage in the url, I just don't care what 
happens. But if something bad really could happen as a result, I'd like to 
know and prepare. All feedback on this is appreciated!

Sarah