The Install of YDL 5 on my PS3 went smooth as silk.
I backed up my HDD data with the backup utility (thanks Sony!), partitioned 10 GB for YDL, installed the bootloader (thanks Sony!) then rebooted to go through a pain-free install of YDL 5.
I then rebooted into the GameOS, which you do at the kboot screen, and restored my GameOS data to its original form.
Not one problem to report. All my downloaded games and demos work, very nice process all around.
In all, I would say the install of YDL 5 took a little over an hour. Backup and Restore took a half hr. each, for a paltry 11 GB of data!
More to come from my full write up for Blogcritics but I wanted to put something down on paper.
