What would you do?

I'd go back to 1970 and spoil the ending of Star Wars...besides of showing people in a cinema my awesome terror/action movie!! (F.E.A.R.)

I would correct some of my past mistakes and visit different time-periods.  For shits and giggles, I'd screw with history's greatest tyrants.  Finally, I'd ensure my mother and father never met.

Let's not allow a causality paradox to screw up a "what if" thread, please. 

but if kain, did go back and stop his mother and father meeting then like you said he wouldn't be born

but if he wasn't born then he couldn't stop his parents meeting

et amendum he would create a infinity paradox that would threaten all of time / space as 2 events that cannot exist in the same time continium would cancel each other out or tear the very fabric of reality

but hey as this is a what if thread

i would

1. remove hilter before his rise to power
2. make sure lee harvey olswald wasn't in dallas texas in 1963
3. stop the 1987 challenger shuttle mission
4. take penicilin back to the 1300's and eliminate the black death
5. stop 9/ 11 by having the terrorists blow themselves up before they board the planes

generally stuff like that

Kind of thought that changing history was the idea, but hey, if we're going down the observation route, I'd go back to check out what the Great Pyramid of Giza looked like when it was just finished, you know, before they used all of the outer stones to build Cairo. I'd need to bring my sunglasses, mind.

Frankly (and very much politically incorrect), I wouldn't correct the 'mistakes of history'. For instance: Seeing the enormity of the historical influence of the Titanic and its fate, knowing it has become a symbol, if a clich?d one, for man's (over)confidence in technology and pioneering, I wouldn't change one bit of it. As a more modern version of Icarus's tale, it's pretty damn good. Most of the wounds involved in the disaster have either healed over time or developed in rich storytelling and (less pleasantly) profitable franchise. Why 'fix' such a 'problem'?
I'm not averse to preventing or ending suffering, but I'd be way more cautious for a lack of knowledge of the bigger scheme of things (if there is such a thing) or what horrendous unknown alternatives might take the place of known problems. In fact, I'd sooner use such powers to stop overeager time-manipulators from leveraging us from the frying pan, into the fire.

of course there would be consequences

but surely not having every girlfriend forcing you to endure titanic is worth whatever happens

I'd go back in time and kill my grandfather before he met my grandmother, therefore undoing one of my parents, therefore undoing me. But if I had been undone, then I would never had gone back in time in the first place ensuring the existence. of my grandparents, blah blah time paradox

I'd go back in time to prevent this thread from being made...

But really I'd go back in time to profit myself but, in different ways, ignoring the question of "How?" I'd try to get more games like Battletoads or Star tropics made, you know the cult classics that even though they have a following don't see the light of day in a brainstorming meeting at a gaming company when they wonder what to make next.

That and I might kick my ass when I was in high school on a daily basis.

Or go back in time before all my NES games were borrowed to see if any of them had a famicom/nes adapter in them, I'd like to see one of those in person...