Money donations can be a way to supplement one's income, but should be treated with low expectations. Visitors are generally not very likely to leave a tip and will only do so when being extremely satisfied with a website.
Asking for tips includes a lot of psychology and following some simple rules can highly affect success rate:
- Don't add donation links everywhere and especially not on shallow posts. Pressurizing visitors into "paying" instead of tipping is likely to have the opposite effect.
- Make a suggestion for an appropriate sum. People often have difficulties assessing the value of digital goods and might not tip out of fear to embarrass themselves by giving too little or too much.
- State a purpose. People are more likely to tip when they know what the money is used for and they can agree on it's use.
One example following the above rules is to simply ask to be invited for a beer and suggesting a donation sum, that will pay for the beverage. Buying someone a drink in order to express a small amount of gratitude is socially acceptable in most cultures (though the choice of alcoholics might or might not be) and also nicely covers up the vapid felling of money being involved.
When using Google AdSense on the same page though, it is strongly advisable to pay close attention to the phrasing of the message. Putting a block in the sidebar, that has the name of a drink in it's title (and potentially some related keywords in it's body), can result in the according page to be considered to contain adult material and being served only low paying or public service ads.