Personally, I always tip when I go to restaurant or when I buy alcohol in a bar, in canada i always give 15% as it is normally what we could give to servers, in Luxembourg, service is include in the price you pay but I always add a little euro or 1.5 euros when the service has been good (i.e not trying to force us to buy more than what we want, a nice smile and a correct speed for the occupation of the restaurant at that moment). For the rest, I rarely tip though, sometimes if the taxi Driver was nice I give him an extra dollar but that is it.