How do you prevent getting bored? And how do you prevent your audience to notice that you're bored giving the same talk for the Nth time?
These are actually my biggest problems giving presentations.
I get bored while practicing (and it’s getting worse as I get better) but the audience changes everything for me. In the absence of special talents, plowing through boredom and practice anyway is what separates good talks from mediocre ones.
I also don't find the rehearsals boring; in fact, around 24 hours before, I'm already starting to get excited about the upcoming talk. So I'm pretty amped up.
One challenge is multiple talks back-to-back. It's hard to keep that momentum up for several days in a row. I've definitely had occasion to give a great, high-energy talk and then give a talk a day or so later that just feels "off", especially in terms of my energy level.
How boring does it get for a painter to use the same kinds of brushes for all their paintings? Or for a musician to use the exact same instrument? It doesn't, because they are not what you focus on.
It may get boring to minimally refactor the same code twenty times -- the code is the focus of the action. When giving a talk about the code the focus is what you want to achieve with people, not with code.
If you are there and really only care about the thing you want to present instead of the people in front of you then sure, they will probably notice.
Disclaimer:
This goes along with the other sub-thread here about the value of recording talks. What I say above is more about talks that are about convincing and motivating people. I don't mean that as in "motivational speeches" at all, but an Apple keynote about their new products is in that category. You want to give people a "look behind the scenes", at the person, because technology fails if the people and/or organization(s) fail no matter the quality of the technology. If the talk is about the latest internal optimizations of the V8 Javascript runtime giving the talk once and then point to the recording, or even just a lengthy blog post may actually be better and the main reason there is a talk is "the conference is there anyway and why not". But that's the kind of talk I would put only minimal effort into and it still works, because I don't need to convince and engage people, only to inform them.