I've spoken at length about Nik Efex in my blog on the creative camera - www.thecreativecamera.co.uk - so I won't go into detail here but I use Silver Efex, Analog Efex and Color Efex a lot in my post processing when I'm looking for strong image stylisation.
The event itself was called Sax on the Beach. The musicians were Paul Scott on saxaphone and Ukulear Fusion on ukuleles. All images copyright Dave Collerton