A/C hiss?

[kierf]

I have an '08 Hatchback, automatic.
Today, I noticed my A/C stopped working. The blower blows, but with the A/C button depressed, it never gets cool and I hear a hissing noise coming from the vents. Once I turn off the A/C, but leave the blower on, the hiss goes away.
I popped the hood and saw liquid on the plastic underpan. It isn't very viscous or very greasy, but it is definitely oily. I have a bad feeling it is the compressor.

Any thoughts?

[CTScott]

Take a look at the sight glass on the AC line just above the compressor. You should see some bubbling in the freon with the compressor running.