Off topic about YLOD, it is definitely true about the heat and turning it off slowly. I live in Cali, so it's hot most of the year, and the room w/ PS3 doesn't have A/C either (don't ask). The fan was making noise a lot of noise for over a year, to the point I actually began to think of it as normal. The other big sign, in hindsight, was that the console would crash randomly (not just playing fallout, lot's of games). Well, I definitely got my $$ worth, I used that console a lot of the many years I've had her.
As far as how long the re-flow lasts depends a lot on how effective you are. There are some people who do stupid things to reflow (some horrible ideas I've seen include throwing the motherboard in the oven, steaming the entire ps3 thru the back vent with a hair dryer and spreading the Thermal Compound with your fingers which can leave oils on the cpu that will fry it). If anyone uses any of these horrible methods, while they might luck out and get it to reflow for a bit, it won't last long - and when it does fail, it likely won't be recoverable again.
If you re-flowed properly - by that I mean:
Dismantling the entire console carefully with proper sized screwdrivers (small Philips, medium Philips, torx T10)
Blast everything with compressed air till there is practically no dust left
Use a lint free cloth with isopropyl rubbing alcohol to remove the old Thermal Compound from both chips and fan sinks.
Apply heat at the proper temperature (650-750 F) from approx one inch away, for around 17 seconds to the proper spots and ensuring it doesn't move for 20 minutes after you finish (per side)
Use a plastic card to smooth out the thinnest line of Artic Silver you possibly can.
If you do that all properly, you can be back in business for years actually, according to the posts I've found. Also, by re-flowing this way, even when it does crash again, people have been able to reflow it again and again and again, thou eventually it just stopped working.
My first crack at it yesterday, I went a bit light on the heat, and I cracked the little flipping part of the lever that locks the Blu-Ray ribbon in place, as I was re-assembling it. It turned on anyhow, and I got it to run for about an hour, then it crashed. I did it again, applying the proper amount of heat this time, and it has been a lot smoother. I backed up the entire thing, which took 15 hours to run (the backup file is over 100 GB), so I think the console might hold up for a while, but I am going to get a slim soon. Some of my shares have a ton of content, and I'd simply rather not risk losing it all.