I just returned from a trip to Amsterdam (2 nights), Haarlem (1 night), Bruges (2 nights), Brussels (1 night), and Rome (3 nights). With good planning, I fit in all the sights I especially wanted to see and left a few for future trips. Here are my quick impressions and tips.
1) Rent a bike in Amsterdam. I'm a walker, so I walked everywhere and located my hotel for convenience (Hotel Piet Hein - comfortable, close to Museumplein, not many dinner options nearby, or so it seemed). The canals make every trip longer than it looks on a map.
2) Everything is closed in Haarlem on Sundays (the day I wanted to rest and catch up on sleep), but that doesn't mean it's quiet. I arrived to find a footrace event in progress that last until about 16:00, beginning and ending in the Markt. Hotel Amadeus - good restaurant, easy check-in and -out, took my credit card.
3) Bruges is wonderful, quiet, and there's enough to see that you can spread it out a few days if you take it easy and enjoy some downtime. I could have given it another day. Hotel Notre Dame - ideally located, very small bathroom, slight mold smell, near a school with a loud bell between classes and loud children.
4) Brussels was too crowded for me, but I only went there to catch a flight out the next morning. The Royal Museum of Fine Arts is worth an afternoon. I particularly enjoy Breugel. Hostel Breugel - it's an association hostel a few blocks from the Grand Place, a few blocks from Central Station, and a few blocks from the palace and museum; nothing else to recommend it.
5) Your magnetic strip credit card doesn't work in the ticket machines in Brussels Central Station (at least mine didn't).
6) My flight from Brussels to Rome was canceled and the next one didn't leave for 13 hours. I got myself on the late flight, but kept my bag while searching out other options. I considered (A) waiting, getting into my hotel very late, and dragging myself around on my first day in Rome; (B) detouring to Paris, spending the day in the Louvre, and flying home the following evening; and (C) flying close to Rome and taking the train. There is a travel agency on the second floor of the Brussels airport (called Connections). They had a morning flight to Florence. I took it, caught the bus from the airport to the train station in Florence, and the train to Termini Station. All together it cost me $500, but given how far I'd come, how long it would be until I could see Rome again, and how most of my next day would have been ruined by the long travel day and late arrival, it was worth the money. Before you go on vacation, your money is worth more than time, but once you're on vacation, your time is worth more than money, so long as you're not on a budget. I'm working on the refund for my first ticket, but hey, it was only $80.
7) Tamara's Suites in Trastevere is on Piazza di San Cosimato and run by two nice gentlemen (one with excellent English, the other fairly good). They were helpful in getting me oriented. The shower leaked under the tiles, and there was a strong smell of mold in the bathroom. But they had A/C, and it worked well (and was necessary). The only reservation I had was that they offered to get me a ride from the airport for 60 euros - I'm sure that was for a private car, but a taxi is 50. When I asked for them to call me a cab my morning out, they called a cab, not a private car.
8) Ask the cabbies in Rome how much when you get in (Quanto costa...?). If they point at the meter, they're being honest - it cost whatever it costs, with a regular drop charge of 3 euros. Try to negotiate for an especially long ride, but for a short one, just watch the meter. Cabs in Rome are cheap and a big time saver (got me to St. Peter's in time for Mass).
9) Food and alcohol is expensive in northern Europe. You can save a few Euros with every meal by not eating on squares, or at least not the main squares.