@Edent
The technical side of microtransactions is simple - anyone can add a button wherever. Getting a payment processor to perform the actual financial transaction has so far been more or less impossible.

The only payment processor that any fraction of people actually use are Visa/MasterCard - and they will change you ~30¢ + %5 per transaction, so you will lose money (be charged more than the tip is worth) on every tip you are sent that's under ~$1.