I adore great typography, but I think @font-face in practice contributes to some of the most annoying user experiences on the web today.
It is very frustrating when loading up a website and seeing a mostly blank page because the fonts are still downloading. This is especially frustrating on a slow internet connection or on mobile.
I'm sure that more people will discover and adopt best practices to improve performance and overall user experience over time, but right now I'm noticing this slowdown very frequently. - see http://www.igvita.com/2014/01/31/optimizing-web-font-rendering-performance/ for some notes on best practices
To me, speed is still the most important feature of a website, and it's shocking how bad this experience often becomes when web fonts are added to the equation.
This is one of the biggest problems I have with the current web because of how frequently I'm noticing this.
Soon to be fixed! Blink (Chrome, Chrome on Android, Android 4.4+ WebView, Opera) will be implementing new behavior for how webfonts are loaded: http://crbug.com/235303#c17 Basically, you'll only see invisible text for a maximum of 3 seconds (this is the same as Firefox). As Ilya's post also points out, we have strong data on webfont latencies in the wild that supports this behavior.
Further, we're shipping it with Font Load Events so you can customize loading behavior very easily. On the Safari side of things, I've seen WebKit add a radar tracking ticket for font loading behavior, so it seems likely Safari will be updating their style soon as well.