I attended a conference a while back, and sat in on one of the main presentations.
It was a great talk, had great content, and the speaker was well known, having written a widely used piece of software.
Overall, I really enjoyed the talk and learned a good amount.
But he did one thing that I found extremely distasteful.
On the bottom of all his slides was a banner ad for his company, it took up a quarter of the screen.
Tacky.