I have a Python SOP which creates a lot of data in the form of points and polygons. I need to be able to create groups of this data within the SOP's code so that I can perform different operations on them further down the network. I couldn't find a method that would let me do this. Is is possible?

Creating groups is currently not possible in HOM. Your best bet is to use an attribute with a unique value per “group” then use Group SOPs afterwards to create the actual groups.

Thanks graham, good to know. I'll go down that route then.

Isn't it possible to call vex from within python and let vex create a group? Or let python create a group node?

It's not possible to call VEX from within Python in Houdini 10.0. In his class in Los Angeles back in March, Luke mentioned that you will be able to run CVEX in Houdini 11.0. However, you cannot create groups and such with CVEX since it is not run in any context and therefor can only really be used to process data.