HTC Dev unlock and S-Off are two completely diff things.
This ICS leak is very very very unstable and very buggy and not recommended flashing unless you have a factory shipped Vigor with S-Off, S-Off allows for a far easier restore if the HBOOT changes, basically if ya don't know what your're doing, don't flash this. S-Off also allows us to re-lock the phone and show a **LOCKED** status instead of **RE-LOCKED** status in HBOOT.
HTC Dev unlock allows for perm root and custom ROM's, this gives us access to write to the system partition.
S-Off allows for flashing of custom radios and kernels (well, since a new script was written, we can flash kernels, but not the way they were meant to in fastboot).
S-Off gives us access to EVERYTHING. Unlocked bootloader gives us access to system partition.
And I agree, I love Sense and the widgets, but I hate that you can't resize them. I think an improved Sense version on top of ICS will be killer.