I dunno if it's just me, but for the anal-retentive bastard in me, I ESPECIALLY hate seeing typos in PDF. Inexplicably, I am much more forgiving of them on web pages, as in HTML files and the like.
There's a sense of permanence to a PDF that just makes the mistake all the more heinous.
http://www.sgi.com/pdfs/4177.pdf
"infrastruture"