Is repair different than how it was in FO3? Because I seem to be able to repair items to very high quality even though I have a low repair skill.

Yes it is. Because they changed how weapons do damage based on repair. Simply put, in fallout 3 weapons did DamageXCondition, whereas in NV they do 100% at cnd75% and up, and then less below that. So yes you can repair everything to 100%, repair is more used to make ammo's and such. Pretty much its much less important than in Fo3. In Fo3, if you didnt have like 80+ repair, all your guns did crap damage, making it a skill you HAD to get up, and that was bad.

The repair skill now just dictates how many of the extra items you need to repair something. As your repair goes up, you'll need less. Any repair level can upgrade to 100%, it could just take 20 extra items to do so.

Is that little marker on the condition bar that 100% threshold? I was wondering what that was. No mention of it in the manual.

Hmm, you're right. I could have sworn I saw it in the manual, but it's not there.

Which means I read it in one of the in-game tutorial screens in Goodsprings. (Maybe during the training mission to kill the geckos around the water?)

Yea I think it describes it in Goodsprings. The little arrows show 75% CND on weapons, and I think 50% on armor. (For max DT)

Repair is good to get up for story options. ED-E for example, can be fixed with a high science or repair skill without needing special parts.

The little repair CND bar in the hud makes it very apparent when a weapon is below it's optimum performance. If you notice, there's a little break at about 75% condition; anything about this, the weapon is doing maximum damage. Any lower, and it will start doing less until it breaks.

The only thing that disappoints me about repairing is that they, just like FO3, require you to use the same type of item to repair. I got so used to mods in FO3 that not being able to repair with Scrap Metal and Wonderglue is annoying XD

There's a perk for that