Aeration and Yeast Pitching Q's

I know there is a bit of debate about whether or not pouring 2 gal of hot wort into 3 gal of cold water causes unwanted aeration and off flavors - going forward I am going to try and cool the wort before combining just to be safe.

However, I've seen many references to vigourously aerating the cooled wort before pitching the yeast. None of the kits I've ever used has mentioned this, but I feel like I may not have been getting enough out of my yeast - airlock activity stops after around 48 hours (I realize it is not the best indication of activity) and I've gotten off flavors (very hard to describe) and so-so beer. Is there anything close to a consensus on pre-pitching aeration? Does it matter if you're using dry yeast (as I have been) or a liquid starter (which I plan to start doing)? Should the act of pouring the cooled wort into the 3 gal of water in the fermenter provide sufficient aeration?

When I first started out, I had similar results, ok beer and some odd off flavors. Once I started controlling temperatures during fermentation I found my beers came out much better. I think moving to a full boil also helped along with a good grasp on sanitation. As far as aeration, I do a vigorous shake of the fermenter before pitching my rehydrated dry yeast when I use it (which is any time that the beer I'm brewing doesn't require a special yeast). Depending on the dry yeast you are using, it may be mostly done in 48 hours, S-05 and Nottingham can rip through wort pretty fast.