Rich, yep that is the default Maxwell "Physical Sky" straight out of the plugin -- you can customize that to achieve many differnt atmospheric effects but I'm not to the point yet where I am ready to worry about that... I'm getting close though
Liam, I'm sure with your texturing skills you will achieve fantastic results very quickly. The key with Maxwell is the materials and on that front you can watch a bunch of my Maxwell videos for free either on the VTC site linked above or on the Maxwell THINK! site (which is a tutorial repository) here:http://think.maxwellrender.com/first10steps.php?categoryFS=21
I also did a very quick(about an hour) intro to the Sketchup Plugin here: http://think.maxwellrender.com/first10steps.php?categoryFS=15
They should help you get up and running very quickly.