Just to go through my own list of Aspects, and my ideas about each one:
New Warden In Town
We actually haven't met too many local magic-users yet, so I think this will get easier to compel in later stories. The game is set in Boston, where new faces are generally unwelcome. So a new face who is also a Warden should be particularly distrusted. The difficulty so far has been that we've mainly met mundane bystanders or people who are already suspicious of us, so it hasn't really come into play that much.
Somebody Has To Do It
I've self-compelled this a few times. I like it as a Trouble-Aspect, but I don't think it would come up too often. In an investigation-style game, you learn about a problem, self-compel ("Well, somebody's got to take care of this!"), and then that Aspect is pretty much done as far as compels go. That's not necessarily a bad thing, since it's done it's job of getting me into Trouble. (But's it's not earning me piles of Fate points either!)
I had thought this Aspect might work by having my character over-commit to lots of different jobs. ("I'm dealing with another big problem right now, but somebody's got to help you!") But we've pretty much been tackling cases individually, so that hasn't come up.
Knowledge Is Power
This is your basic "Indiana Jones" Aspect. Sacrifice the Ark of the Covenant to save the Girl? Hmm... Tough decision... This could come up more later, but so far we haven't encountered any fonts of knowledge or interesting relics that I'd need to defend. It could be that the GM just needs to leave more ancient texts lying around, but I'd be interested in ideas for how to fit "Find and protect knowledge" motivations into a "Solve This Crime" storyline.
Been Around A Long Time
I've talked about this a bit already. The character is a two-hundred-year-old White Council veteran. He's been around a long time, so he's got plenty of backstory. The plan is to start compelling complications as we meet new people ("Oh, by the way, the local head of the White Court? We used to be engaged... Fate Point Oh, and I killed her brother... Another Fate Point") I think I could get some good mileage out of this one, but since we've only met "small fish" so far, I haven't been able to think of a good compel for it yet. Plus, I don't want to overdo it. ("This nurse was just attacked by a ghoul!" "I... uh... knew her father?" "Dude, you can't be connected to every random person you meet."
Stubborn Old Mule
This aspect and the next one are the ones giving me the most trouble. We've been running investigation-style stories so far, by which I mean they follow the pattern: "Learn about a problem" --> "Investigate the source of the problem" --> "Deal with the problem". Since the plotline is fairly linear, I can't think of any way that being old or stubborn could make things more interesting. It seems more likely that they would get in the way. Until someone tries to stop me from doing something or pursuing someone, the Aspect will just be sitting there, gathering dust.
Needs Of The Many Outweigh The Few
So far the needs of the many and the needs of the few have been pretty compatible. Random guy is killing people with magic? He should probably be stopped. I think both individuals and the overall majority would agree with that. I think the problem may be that these two aspects, while interesting, seem particularly dependent on what the GM throws at me. Is there a way to design Aspects that are more story-independent? Should you design Aspects to be story-dependent, or is it the GM's responsibility to bend their storyline to hit your Aspects?
(plus one more I plan to replace anyway)
I think I'll take Sanctaphrax's advice about "unwise combat decision" Aspects. I'm leaning towards "Always Give Them A Chance", which would compel me to waste a turn at the start of every combat to ask for a truce/surrender/etc. Plus he would generally be against ambushes (unless he'd already offered the enemy a chance). What do you think?