Every page will be signed by a key and our browser will show the popularity and karma of that key.
The popularity and karma of a key will probably be readable on a blockchain, similar to the account balance of a Bitcoin address.
If one was to download a popular software and then sees the website is not signed by a popular key, they would double check if they are on the right site.
Karma will probably be a customized value. Counting the opinions of my friends over the opinions of my friends friends etc.