The data comes from a variety of sources including the UK Mettoffice. I always compare the output of Jepp against the Met Office site and have always found the data to be the same.
Jeppesen do make mistakes but they seem to be getting fewer these days. I have certainly not seen any discrepancies between flight star and my paper versions. In fact things like frequency changes are usually faster than my paper updates.
The Jeppview approach plates software is very accurate and certainly no errors between my paper aerad and the jepp plates have popped up yet.
At the end of the day I never forget it is my responibility to verify the information.
I have Nav Box ProPlan5 and it is pale in comparison to flight star!
Avbrief is a pretty good site. I have just gotten used to having everything integrated!