I've heard there are negative effects of oxygenating wort before a boil. I don't lauter right into my boil kettle, but just dump the wort into it when I hit my target volume. There's a lot of splashing going into the boil kettle, can somebody explain what effects the pre-boil oxygenation will have on my beer?
Little to none, most likely. Between boiling most of the oxygen out, putting more oxygen back in, and then the yeast multiplying and eating up whatever is in suspension, it's really not something you need to worry about.
You should definitely be concerned about excessive oxygen post-fermentation, but I don't think it matters much on the hot side.
What you're asking about is usually called "Hot Side Aeration", or HSA. A few years ago, there was a lot of concern about HSA and people thought that excessive mash stirring or splashing could lead to early staling of beer.
Recently, opinion is that HSA is just not a big deal for home brewers. It's something that large, commercial breweries might have to worry about. But on homebrew scale, it's just not a concern. An older column by BYO's Mr. Wizard explains why as does this more recent episode of Brew Strong with Dr. Charlie Bamforth.
The Brew Strong episode is well worth a listen. Bamforth knows his stuff and he really breaks down the science.