The notes are just ridiculously colorful (anyone who says they look like monopoly money is not far wrong) and some of the coins come in different designs based on the country of issue. One thing to note though is that with the current exchange rate ($1:€1.2 at writing) those coins do add up. Make sure you spend them before you leave so as not to get caught with $50 worth of change you cannot convert back when you return.
Of all the places I have visited I still think the Euro is one of the more bizarre.
The tipping culture in Western Europe is pretty different to that in the US. Servers are better paid and as a result a tip of around 10% is common. For a taxi ride tips are not generally expected, just round your fare up to the nearest Euro. If a driver is especially helpful (most will have plenty of ideas for things to do and sites to see) don't be afraid to tip up to 10%. Most bar staff prefer their tips in the liquid form.
Dublin is a fascinating city with tons of historical sites to see and with entertainment options for all the family. For a true taste of the city though you will need to find your way to the centrally located Temple Bar District for your evening's entertainment. This is the place to enjoy music (both authentically Irish and also more modern) as well as having a beer or five with the locals. As with most European cities the public transport system is excellent and you will never be far from a bus, taxi, or light rail station. This means you can enjoy your time at places like The Porterhouse and The Foggy Dew to your heart's content.
The number one tourist attraction in Ireland is the Guinness Storehouse in Dublin. Go there and see how the stuff is made, then try a perfect pint for size.
Watch a Rugby Game
Obviously this might not apply for all, but anyone who has transport available should think about travelling to Belfast in Northern Ireland to watch The Opening match of the Pro 12 League as Ulster takes on the Glasgow Warriors. This trip takes about two hours by train (1:45 if you drive) and the match itself is a game at the highest professional level of the sport. What better way to prepare for Navy beating Notre Dame than by taking in a game of the sport that gave birth to football in the first place!
Temple Bar in Dublin.