3D modeling and printing can be easy if you have the right tools and programs. My experiences with the free Sketch Up Make and the Makerbot Replicator 5G printer are quite positive.
Getting started with 3D modeling:
Download and install Sketch Up Make (if want the program in a language other than english be sure to visit the webpage in the corresponding language) For example, http://www.sketchup.com/de leads to the German version.
Download and install the software for your 3D printer (in my case, the Makerbot desktop).

Sketch Up Make model of a gear from a Hexbug spider robot. Gears have been drawn with the Involute Gear plugin.
Start Sketch Up make. If you get an annoying prompt every few minutes, start sketch up make with administrator rights until the demo time for the Pro version is over.
Usually, 3D models are printed from an STL file, so you need to install the STL export extension. The extension can be found and installed via the extension warehouse. The extension warehouse can be found via the Window menu of Sketch Up. For accessing the warehouse extensions, you need to log in with a Google account.
So far you can draw and export STL files.However, these files often suffer from model errors like inverted surfaces, holes, etc. In order to repair these problems, we recommend to run the STL file through the model repair service from NetFabb. The service is free for non-commercial use, but requires to sign in with a MSN ID to be used. Upload your STL there and download a repaired version (unfortunately there is no feedback what has been repaired).
Finally, open the STL with 3D printer software and hit print! Happy printing…
… and waiting hours for the printer to finish.