In FO, you have to use the perk when you level up.
In DA, you store the skill point until you want to use it.
I really enjoyed the DA method far more. A couple of reasons are this:
1. It allows you to store perks, until you know what direction your character is heading. Why spend a perk, thinking your going to love marksman, then figure out later that it doesn't suit you.
2. It allows you to meet perk req's and then spend the perk on that tree. For instance, a perk in sneak req's 50 in sneak, but you're at 47. Store the perk, then use it when you hit 50.
There were times in FO, where there wasn't a great perk option...so you took the best thing you could think of. But some of the VATS perks went wasted as you progressed. I like this for the fact it will make for less powergaming and is probably more "realistic".
I can see both sides, although I favor the DA way of doing things.
Thoughts/Opinions?