In some restaurants I found that the 10% tip was included in the bill, which is something I dont like. I understand that I should tip someone when I get a good service and not because I am obligued to. I do not get tipped for doing my job, I mean, so at least let me decide whether I want to tip someone and how much I want to give.
Dublin has come a long way recently when it comes to tipping - Although I believe many American tourists are told not to tip as it is not expected, I can assure you that in some cases it is! In general, behind-the-bar staff in pubs/clubs will not expect tips, but if a lounge-staff member is serving you it is common courtesy to tip for being looked after. Also, if a large group of people has been well looked after for a prolonged period (ex all evening) by a behind-the-bar mamber of staff, tipping will be expected (not necessarily 10% though - a token fiver or tenner will be greatly appreciated.) Tipping in restaurants IS now expected - 10% is the norm. Tipping taxi drivers is discretionary.
Tipping for restaurants may be included in the bill for large groups, but otherwise, is discretionary. 10% or more is sufficiently generous. Tipping floor staff in bars is always a good way to get good service for the rest of the night, but isn't necessary for behind-the-bar staff. Taxis and hotel staff is more up to yourself, but a little is always nice.
Don't worry about being over-friendly if in a Irish pub. If people have no interest in chatting, you'll know by their response (or lack thereof). But if you do get talking to someone, NEVER mention Northern Ireland - can of worms to say the least.