The break in slides are primarily for aging the panel evenly and applying D Nice's settings.
The only thing they help with IR is just blowing through the first 100 hours or so faster, as sets are more prone to IR early on. Runnin the slides doesn't make them more resistant to IR after 100 hours than if you just watch full screen content (avoiding static images like logos and letter box bars) foro the first 100 hours. You just hit 100 hours faster if you run the slides 24/7--or over night and while at work etc.--than if you just use the TV normally.
It's also a way to look for stuck pixels, detect buzzing etc. and otherwise make sure your TV is ok by putting it through the paces right away so you can get it adjusted and make sure you like it before the return period is up.
As far as IR--that just seems to vary on whether people get it, and whether it bothers them (as almost all is temporary, and the majority goes away pretty fast when watching other content). For me, I was getting a good bit from ESPN and CNN, and even more from games. It all went away after a few hours of watching other stuff. But still annoying. Mine (a UT50 55") buzzed loudly (to me) as well so I ended up returning it and getting an LED. I loved the picture quality on the plasma, but just couldn't tolerate the buzzing or worrying about IR since I do a ton of gaming and watch ESPN for hours on end.
But mostly, the buzzing just varies by panel and a persons hearing and IR is not a big deal for most people as most people mix up content enough that it will never be more than a temporary annoyance. So I wouldn't worry about the IR unless you're doing marathon gaming sessions or leaving it on channels with tickers like ESPN for hours every day. Just be a bit more careful with static images and black bars the first 100-200 hours to avoid IR and age the panel evenly and then you're probably good to go.