I don't actually agree with the 'no tipping' custom. Finnish people might not tip very often, but when they do tip, they show that they liked the food, the place and the service - just like anywhere else in the world.
You are not obliged to tip a certain amount (e.g. 10-20%), but as a general rule, I leave about 10% tip, if I am happy with the service and usually there is nothing wrong with it. I actually consider it rude not to tip.
All waiting staff have an hourly wage, they are not expecting you to tip. In some restaurants, they do not know what to do with tips, so you may be tipping the owner rather than the wait staff.
Feel free to leave a couple of coins with the bill or some of the change if you like the food and are feeling generous but more then that, it´s just silly.
Although of course no-one is going to say no to free money... so if you want to overpay for your food, no-one will complain.
Do also note that evenings and weekends are especially well paid (50% extra wage after 6 pm, double-wage on Sundays) so if you feel like tipping, the best time to do it is during weekdays as the waiting staff will have the smallest income.
Just a good thing to remember when you're sitting in Pizza Hut wondering why you are spending 9 Euros on Pizza... THAT'S ALL YOU'RE SPENDING. TIP IS INCLUDED.
Oh yeah, and water is free....
look, I had been in Russia for two months - where if the water is free, you DON'T DRINK IT.
In Finland generally all the service charges are included in restaurant, hotel, and taxi bills. But of course the waiters and waitresses are pleased if you leave them some change. But Finns don't do it normally.
Don't bother tipping the bouncer at any night clubs. The only reason for doing so, is to make him remember you so that NEXT time you can stroll past the queue. And the only way for him to remember you is a huge tip or tipping frequently enough. But you're a tourists - how frequently do you visit the same club to make it worthwile? Otherwise tipping is OK (about 10%), when you get good service at taxis, restauraunts etc.