Lame_Wolf - 6:42 pm on Sep 23, 2012 (gmt 0)

1. Why doesn't AdSense implement in-text ads? Any ideas?

Because they are crap?
I'd never use them. They are a PITA for the user.

2. I've been using a combination of AdSense and Infolinks for a while. A fellow webmaster recommended me Kontera instead of Infolinks. Does anyone here use Kontera? Do you perhaps know how it performs compared to Infolinks?

Sorry. I only use Adsense.

3. Whichever ad provider I use, they seem to load "forever" -- meaning that they considerably slow down the loading time. Any way to prevent this?

Doubtful. Have you tried them on a dedicated server?