Here is a list of sites, downloads, tips, tricks and hacks for Logitech Harmony universal remote controls, mostly for Harmony One.
Don't use the software that came with remote. Download last version from Logitech.
Print this worksheet when you go hunting for model numbers of your devices.
Check if your devices are compatible with the remote.
Great database of channel icons for use with “favorite channels” feature.
Some more tips and tricks.
Use some models on Linux (but not One).