Hi GiWiz!
Speaking from experience, it is easier to travel with an infant than an older child. But -- first make sure that the cruise line will allow a 5-month old to cruise. Most lines have a minimum age of at least 6 months, although some will make exceptions.
Our son was 11 months old on his first cruise, and we had a wonderful experience. We brought a lightweight umbrella stroller, which was essential for getting around both on the ship and in port. (We carried him into the dining room though, as space is usally tight.) Waiters doted on him, as did several passengers. Should you go, it's usually better to opt for early dining as that is when most families dine. If you are concerned about other passengers, as we certainly were, request a table for four in the dining room.
I'll be happy to answer any other questions you may have. And, welcome to CruiseCrazies!
Edited to add: The fact that you asked about experiences with other passengers' infants shows me that you are a considerate person, so I doubt your young one will create a bad experience for others.