You could definitely still use Amigas these days to do a lot of useful tasks. 2D graphics, 3D, audio, video titling, DTP etc... The PC software has left the Amiga equivalents behind, but that doesn't mean they still can't produce some great results. It just means they are missing the current range of features found in the latest software on the market.

As for Amiga still being used in a professional environment, I did see something about them still in use at NASA quite recently, but I'm not sure if that is still the case. It would be interesting to find out if they are still in use anywhere.

The London Transport Museum used a large bank of CD32's with SX-1 modules until recently to power their interactive kiosks around the museum.