Zango will send the anti-spyware warnings into a fit and issues many warnings, if people have the anti-virus running then they will most likely have to turn them off to install the toolbar. They pay varying rates based on the country of origin - of the installer, 75c for U.S, Canada and U.K 50cents, then it goes down to 0c for vietnam, afghanistan and similar countries, the actual pay for installs can be even higher based on the number of installs - for instance if you go over 5000 installs then the price increase by more than 20%.
The tier is actually 3k-15k installs/month then you get a bonus with installs. For me with zango I made $1,125 in one month which actually came to $1,525 due to being in that tier. So you get a pretty big boost if you can reach the higher tiers.
Same as MLM (multi level marketing) pretty much however they should give affiliates residual income percentage from all sales then we would be making really BIG MONEY