Wow, more fantastic replies... I think I'll be sticking around here
@ledisnomad: my intended use is - for the moment at least - to play! I work mostly in web design / graphic design, but I'm a bit of a jack of all trades (i.e. master of none) so I'm always happy to have something else to add to my CV. 3D modeling wise I'm interested in archviz and potentially organic landscapes - I've seen some amazing stuff done with instancing and indigo renderer.
Fun is definitely the keyword here - personally I tend to try and turn things I enjoy into a potential career (see the CV comment above!) which sometimes sucks all of the fun right out.
However, based on you guys and gals I'm going to stick with Sketchup! I had a peek at the 'get started' guide for Maya and threw up a little bit!
Next up is a thread asking for your recommendations for 'must have' plugins - i.e. what every newbie should have!
Thanks everyone for your views!