Here's the numbers I ended up using:

• Cab - About 10% is a good baseline. We should've tipped more heavily for our driver in Dublin, who broke the rules to get us to the train-station on time.
• Restaurant - About 10%, plus a little rounding-up.
• Pubs - No tipping. For extraordinary service, you might buy one for the pubtender, but Turly assures me this is a pretty rare thing.
• Hotels - Only if someone carries your bag. We never encountered it, so I'm not sure of the rate.