I would keep it on in the rain especially if you're on stock tires. I nearly hit a curb taking a turn at speed in a light drizzle, the car started hydroplaning mid turn.

If it's not wet the car has not enough power to put you in danger, unless you do it on purpose. As for my own experience (little experience), if you don't break hard in the middle of a turn or you floor it in high revs there won't be any trouble.

Pouring rain on highway i leave it on. Other then that it is always off. Incase of an emergency I can save my self and not be limited by the driving aids.(Need to **** it out of the way if someone is about to hit me or something of that sort) Just makes it like im driving an old car like I am used to.

The TCS and ESC systems aren't replacements for proper driving. You shouldn't rely on them to save them from any situation. If you often times have issues on wet roads, and these systems are intervening, you are probably driving too fast for the conditions.

after i got my Phantom ESC, i turn on VSC mode most of time. whenever i need to take turns little faster, my tail slides a bit lol
rainy days, i usually leave everything on
i need to get proceed module for my setup which is better than throttle switch i have

This is where my concern comes into play on this subject. The older guys that drove many cars before this existed and the younger guys with plenty of track time can turn this off and fully understand what will happen. The younger guys that have really only experienced FWD and have a bit of "spirited" street driving behind them have no clue how fast things can go bad with the system turned off.
This whole "the car is not powerful enough to get into trouble unless it is wet" mentality is crap and can end up with people hurt and cars damaged. If the system is kicking in then that means that you have pushed the car to it's preset limits and it at least attempting to save your ass. Yes, the nannies limits may be lower then what the real limits of the car are but if you are hitting them on a regular basis on the street them you may need to review your driving style.
I know that everybody here thinks they are professional race car drivers but things can go wrong very quickly if you start hammer your car on public roads. On the track cool, pull the bloody fuse and have at it.

Tcoat, I've never owned a FWD car. Well except and RSX-S as a daily for a little bit.(changed my outlook on FWD) But i have a bit of track experience(drifting, plan to extend that to a little road course stuff with the brz). And know my limits! The Brz being my first new car makes me very cautious driving it anyway. I never really drive in a reckless manor in fear of crashing it. My car has plenty of power(turbocharged), and when you have coilovers on these cars it seems the nannies are a bit more sensitive, For example if 1 wheel loses contact with the ground the nannies have a spasm.

LOL I wasn't going after you. You just made the very good point that you were used to older cars and how they handle. This is important since many of the guys that are not used to RWD and how it can act read what some of the others write and think it is all easy and great. It is when you know what you are doing but can be horrid when you do not. They need to learn the car's limits with the traction control before they start worrying about turning it off all the time.

Not saying they were or that I relay on them, just saying for certain situations they can be helpful or an additional safety measure.

after I hydroplaned in my MR2, I was scared of rain lol. thankfully it was during braking and in a straight line when I felt my steering completely go light. sketchy as hell for me since all I could do was stare at the cars in front of me and keep the wheel straight while not inputting anything. it was a 1986 so no electronic assists, but maybe if I had assists I don't even know if it would have made a difference.

the downpour came out of nowhere too, in the desert where it rarely rains and all of a sudden it rained so hard in the middle of the day. having RS3's probably didn't really help that much either. my driving in the rain is cautious especially because of that incident. and the fact that I run summer tires all year long so I am even more careful the few days it rains in the year.

I only turn mine off when my dog steps on it...

I still get enough slip and slide for my experience level with everything on.

Almost every drive...Turbo plus TCS on is bad
*minus snow, ice, etc*

Since 99.9% of my driving in the FR-S is commuting I usually leave it on, even when driving in manual mode.

I do, however, consider the traction light my arch-enemy and feel it is my duty to make it go off like a madman on occasion.

I turn it off everytime I start it. It's become a habit now.