Black Project: You should start sliding immediately after using the key card. Just slide against the door until you fit through it.
Flying, what were your timings on going to bike school before rather than after Meat Business? It's quite counter-intuitive that setting up before it could be faster.
Flying, what are your reference points to get off the roof in Home in the Hills and the final wave in Home Coming?
That's fine, you gain control while the screen is still dark.
Thermal goggles happened. ^^ http://gta.wikia.com/wiki/Thermal_Vision
There might be consistent and inconsistent spots. My spot might have been consistently without any effect, leaving the 50/50 chance.
Highlights, anyone?
I only watched Just Business and that looked fine to me.
This might be useful for "in-game hundo" (where you need to get 100% completion no matter how). Start a bunch of Quarry instances, start Vertical Bird with those still running, complete it. I have not found out how to consistently avoid a softlock at the start of Vertical Bird, though. Also, it might crash with more than a few instances.
The "Interesting Vehicles" (R¤ naming) list has two slots, so your old vehicle gets "pushed out" if you get into both the Dozer and the cement truck. My guess is that after that, your old vehicle is treated like traffic. Probably there are multiple factors involved, distance, time, you can "despawn" it.
The fastest route I am aware of is: Flight School Stowaway Casino until FIAB get om0 call, hold through Madd Dogg Misapp x2 BP x2 SMB
Maybe getting the om0 call after rather than before Madd Dogg is faster.
Do you understand why they sometimes refuse to pick up the "2nd dossier" in Misappropriation?
http://www.speedrun.com/post/oull2 According to my testing it's almost frame-perfect - 2 frames maximum.
LS duping is possible but it seems to be frame-perfect so whatever.
What S. said and 100% progress with all girlfriends and almost full any% (maybe without Woozie skip, unless beating Saint Mark's unlocks LV shops) until Saint Mark's.
Also, is there a limit to how many clothes you can possess?
I always take the call in the little fade before the intro cutscene starts. Then I shoot to "invalidate" and hang up. I do that for every mission, except that I hang up during the cutscene if I want to dupe.
You get teleported to Katie if you die up to 1500 units away from her house (the map is 6000x6000 units large, afaik). It seems to me that your post does not contradict that. I do not know about Barbara but probably the rule is the same, maybe with a different number than 1500.