If you've been modeling in SketchUp for any length of time you know how it is. You get back from lunch and get stuck into a model for a couple of hours. The next thing you know it's dark outside and your wife is calling you to find out if you're working late again.
It is so easy to get stuck in the minutiae of a model. A model you thought might take an evening takes weeks as you explore every last detail. It is easy to forget one of SketchUp's biggest strengths - its speed. It's an interesting exercise to challenge yourself to model as fast as you can and this is the idea behind the speed modeling challenges on SketchUcation. You generally have 30 minutes to start and complete a model based on a theme and to submit it to the forums for judging. I've only taken part in a couple of challenges but in that 30 minutes you learn so much about how to pare down to the essentials, forget about a few of the details, and build something quickly. There's no time to search for tutorials on how to achieve some specific, niche effect you just have to get the idea of the object into SketchUp as quickly as possible.
Even if you don't submit your model to be judged I do encourage you to try this exercise once in a while - to complete a model in the 30 minutes or less. It will help you to reinforce your strengths and what you already know. At the same time it will highlight your areas of weakness - the things you need to improve on. Give it a go and test yourself!