The software is simple and fun to use. You can build from a limited palette of bricks (still hundreds to choose from) and actually order the set you build from Lego. Not cheap but amazing to get your very own Lego design in the post! You can also upload your design to the website so others can buy (or copy, or even improve) it.
Removing 'filters' in the brick collection allows you to use even more pieces and colours - but not upload the design. I guess there is a limit to the number and type of pieces that Lego has alloted for Factory models. You can still save the design, building instructions and pictures of your creations. Beware - homemade designs come out a bit more expensive than the shop bought equivalents, especially when you use intricate combinations of unusual pieces.
Here are a few I have made:
A copy of the rare set 20004 - Indiana Jones Jeep (given away with Brickmaster magazine in the United States) :
A poor substitute for 886 - Space Buggy - released in 1979. (note the limited palette of colours for some of these pieces:
And my first elaborate construction: a Toyota Landcruiser type vehicle for the State Emergency Service:
