Nothing annoys me more than clicking a link and then realizing I just clicked on a pdf file. Ok, there's actually a lot of things that annoy me more than that (like when I'm typing in one window, and xp suddenly decides to open another window, stealing whatever I was typing). But this is something I can do something about (unlike those stupid windows stealing focus).

In Firefox/Mozilla, there's a handy file called userContent.css, which is basically a big css file you can use that gets applied to everything. But it's wonderful and magically good. The file appears in your documents and settings directory, somewhere like:
C:\Documents and Settings\nathan.tolbert\Application Data\Mozilla\Firefox\Profiles\default.w4n\chrome

Anyway, there's lots of places on the web that tell you little tricks you can do with this file. Someone on slashdot recently pointed out this one, which solves the problem of how to handle those annoying pdf and doc links, by placing a warning right next to the link!

Anyway, enjoy

/*  give a warning if something is a PDF or a DOC */
a[href$=".pdf"]:after,
a[href$=".doc"]:after
{
font-family: sans-serif;
font-weight: bold;
font-size: 0.7em !important;
vertical-align: top;
}

a[href$=".pdf"]:after
{
content: " [PDF]";
}

a[href$=".doc"]:after
{
content: " [DOC]";
}