I've only got working experience with the GECK, and level design is my specialty there, building houses and such, just building in general is something I consider myself fairly good at in the GECK (My signature has some example work, if you're interested).
I've done some scripting in it, and by some I mean I've made a script that shows the barber menu in Fallout New Vegas so that I could apply it to mirrors, that way you can change your hairstyle at a mirror basically. That's the extent of my scripting knowledge, but from what I can tell it's not really like programming. I'm trying (And failing) to learn Java at college so take that with a shovel of salt.
I wouldn't say the learning curve is too steep though, it depends on what you want to do with the tools available. In my experience, level building is very easy once you grasp the controls of the editor and you have some patience. Dialogue and questmaking in the GECK is quite a bit trickier for me, I've got no issue writing dialogue, and I have made quite a few working NPC's back in Fallout 3 (Unvoiced though).
I don't really like working with NPC's simply because I feel like they're out of place without a voice, and without the equipment to do quality recording I don't want to do it at all, if I can't provide quality audio then I'm not even going to bother doing it basically.
The new tools could be much more intuitive though, what I've heard so far about Radiant story makes it sound like every quest modders wet dream, only time will tell.