I am using the default WordPress twentyeleven theme with no other plugins activated. For highlighting the code, I am using the
<pre class="brush: code"> format.
At first the plugin didn't work at all, eventually I found this was because wordpress was stripping the classname from the pre tag. So you need to edit kses.php to allow adding a class to pre. I didn't see this mentioned in the installation instructions, though maybe I missed it. I think that having to edit the wordpress core files is generally frowned upon though.
The other problem is that, now I have the plugin working, it is not wrapping long lines. Instead it gets a horizontal scrollbar. The line has plenty of spaces in it where it can wrap, so I'm not sure why it won't wrap?