The Acrobat Pro X 10.1.1 update came with the facility to 'lockdown' the 'Welcome Screen' (that is, get rid of the darned thing).
(We're talking Windows here. Mac users have always been able to 'switch off' the Welcome Screen).
But the facility is hidden away in the release notes and involves a registry hack.
Trouble is, Adobe messed up the registry hack in the release notes and it doesn't work.
Here is the proper, corrected reg hack: