I always have one suitcase full of donations, usually school stuff and a few clothes (which I take the tags off)... no gifts. I tell the truth but have not tried to bring in a PS3. I would think that a certain amount $ wise is fine to bring into the country but of course the government has to make their own money so that is why duty is charged when bring goods in.
I do remember a previous thread about duty on goods and I believe it was mentioned that it can be quite high. I wouldn't lie though, getting caught is not worth the hassle, imo. I believe the immigration form has a section on the back to list the items that are not yours that you are bring into the country (and leaving behind) and this is where I always list my donations.
You can always try to claim that you are bringing it down for your own use but if you don't have any games with you, it will be hard to convince customs that it is yours to use while on vacation and that you will be bringing it back home with you.
Even though you did not pay for them or you don't see them as gifts, customs may very well just see them as gifts as you are giving them to someone else, even though it is a favour for a friend.