Be aware that the latest version of Blender may have some kind of problem with the Collada importer. I wasn't able to get a Sketchup model into Blender 2.5 beta, but I could get it into 2.3 without issue. I didn't try the latest stable release (2.49).

During my experiments, I found that the Sketchup models from Google's data warehouse were enormous in Blender. So if it doesn't appear to work, try dollying your camera way back. Also, Sketchup exports really rotten topology, so if you're planning anything fancy, you'll want to set aside some time to retopologize. I eventually wound up using a plug-in for Maya to import the .skp file, and I had to spend about three hours per model cleaning them up. Still way less than I would have spent trying to model them myself, though, and their relative scale was reasonably accurate.