The wiki describes how to set up OOPHM with the 6.1-series, but what if I want to develop a widget with the 6.2 which is currently being developed? The wiki states that I need to get the vaadin-oophm-6.1.3.zip file and and replace the default jars with the ones provided with the zip, but where can I find the oophm zip for the 6.2 nightlies?
Use the exact same instructions for Vaadin 6.2 series - download 6.1.3 and use the use gwt packages from there to build 6.2 based widgetsets. Intuitive, isn’t it? 
If you have any questions - please ask them on forums. OOPHM is still quite tricky to set up in its “pre-release” state and it would be great to be able to document any problems with it here.