You should assume there's some users that switched to CSSU, and others not yet noticed they should have done.
Anyway for you as an app-developer there are definitely no differences you need to take care of, since CSSU is 100% compatible to stock maemo regarding all 'usual' apps (== those that don't need CSSU-only functions like portrait mode or whatever, or have to deal with new features like multiple partitions on uSD which might be relevant for filemanagers etc)

btw thanks for (N900-)Fahrplan, it's still one of the apps I use most, right after dialer and xchat.
Fahrplan still doesn't check for accuracy of GPS fix, so you could start searching for your location while "fix" says you're somewhere 3000km off from where you actually are, but hey... patience is a good workaround. *)
However a means for *stopping* GPS when you don't close Fahrplan since you want to look at the route during travel would help a lot to save battery. Probably you could stop your location request (which in turn starts GPS) as soon as (and as long as) user opens route detail display. Then re-enable it when user closed detail view and returns to main screen

*) [edit] maybe a permanently visible icon in top bar of Fahrplan showing actual *accuracy* of GPS fix, instead of the notifier "GPS now available", was a feasible solution to this issue.


cheers
jOERG