So I've noticed that there are a lot of things that if you screw up, they're gone for good. The two that have happened to me are during the Wasteland Survival Guide and the bobblehead in Raven Rock. If you lie to Moria at any point during any of the quests, you fail to get the achievement even if you complete all optional quests. I accidentally lied since it was the first dialouge option and you sometimes choose things you don't mean too and I didn't know about it. Raven Rock; I missed the bobblehead and only later found out it was in there. And since

that bobblehead is gone forever. Which also means I can't get the achievement for collecting all 20. So are there many other items/quests/achievements like that that become lost forever?

What platform are you on, can i assume 360?
"Head of state" if you give up the location of the temple of the union ill do some research and get back to you unless someone answers before i do.

I'm on the Ps3 And I just completed Head of State actually. It was so damn satisfying killing the Slavers who took over the Lincoln Memorial with Lincolns Repeater. Total poetic justice.

Warning many spoilers!

1 bobblehead of strength if you blow up megaton without getting it.

2 bobblehead of medicine if you dont get it out of vault 101 before completing "the GOAT" Or "trouble on the Homefront"

3 possibly all questlines between "escape!" And "Tranqulity Lane" if you just go to smiths garage out of the vault 101, or you complete them all.

4 "big trouble in big town" if you enslave Red in "strictly buisiness" before completing big trouble in big town.

5 "the nuka-cola challenge" if you kill sierra petrovita before completing the quest.

6 "the superhuman gambit" if you kill uncle roe, unsure if you technically fail if you kill/stop the antagonizer and/or the mechanizer before talking to uncle roe.

7 "the wasteland survival guild" and "the replicated man" if you kill pinkerton and/or (dr. Zimmer only in replicated man)

8 unsure if you can fail "oasis" if you attack the branchtenders

9 "the power of the atom" unsure if you can fail by disarming the bomb before being asked, almost certain you can still do it.

More to come. And how do i put things in a spoiler box?

Alright. That's more than I expected. Thanks a lot. I just finished "Take it Back" and beat the game so now I'm going around and doing all the sidequests.

Alright if you want the trophy list http://www.playstationtrophies.org/game/fallout-3/trophies/
Using some deductive reasoning and finding out if any of the quest related characters can die can help you deduce whats what.

Or you could just play it again, and do what you didn't do. It's a bad sign for an RPG when you can complete everything in one playthrough.