Austria has nearly an infinite number of dialects. The main ones are:
1. Wienerisch - spoken in Vienna. Most Austrians detest it because they think that the Viennese people are annoying. It is the most comprehensible one for the German speakers.
2. Tirolerisch - spoken in the state of Tirol. Very hard to understand.
3. Vorarlbergerisch - spoken in the state of Vorarlberg. IMPOSSIBLE to understand - sounds like the Schwitzerdeutsch that is spoken by the Swiss.
Each of the three dialects has many variations. Other ones (Kärnterisch, Burgenländerisch, etc.) are easier to understand and harder to distinguish. Please note that the whole of Austria has less inhabitants than NYC. Most Austrians can easily switch from "normal" German to their home dialect (especially noticeable when students living in Vienna are phoning home to their parents), but a few do have problems in writing proper German.
The author of this article (WojPob) is a foreign student living in Austria.