Twitter & Facebook login details periodically forgotten Amongst others, I have Facebook and Twitter apps installed on my HTC Desire running Cyanogenmod 7.1. 

Every few days, it requires me to login again, even though I've previously saved my details. It even asks me again (for Facebook) about syncing Contacts to my phone... it's as if it's forgotten my login to those apps altogether.

I have these 2 apps installed on the SD card, so wonder if that's the problem - I don't have space to run them from the phone as that storage is very limited on the Desire...

Any ideas if there's a setting of some sort that I can change so that it keeps my details?
Yes, it is likely to be the problem. I suppose it's a hack of yours if these apps are on SD rather than internal memory.

As the Android SDK mentions1, applications that use Service, AccountManager and Widget shoudl not be installed on SD card. The Facebook app has an AccountManager, a widget and a Service.