Here in the Republic of Ireland they have recently dropped the €8 charge for bikes on trains and they now go free but there is officially a limit of two bikes per train which isn't always enforced but I've had a couple of officious train drivers make an issue of it. On the train from Killarney, a popular scenic town in County Kerry bikes are only carried at the drivers discretion and we had to leave them behind on one occasion to be forwarded on to Dublin the following day for collection.
On the local Dublin commuter DART train you are allowed bring your bike on free outside of the morning and evening rush hours.