I took the Scandinavia and Russia cruise on the Royal Princess in June 2014 using the "Northern European Cruise Ports" guidebook. Here are some updates and amendments that may help:
Copenhagen:
The ticket machine at Orestad station only takes coins or credit card. Since day passes cost 80 DKK, you may need to buy something at a shop for such a large amount of change.
Validate the day pass using the same yellow, clipping machines for klippekorts. (This may change soon.)
The Royal Danish Porcelain shop hasn't had a museum for the past three years.
Pickpocket alert around the Christiania area. When visiting Christiania, be extra careful to avoid the aggressive pickpockets. Unless you have a special interest, you may want to avoid the area altogether.
Oslo:
The tram stop in front of the central train station is now closed. Follow the map posted there to find the location of the new one.
There is no more pedestrian bridge to the opera house from the train station. Just follow the signs/crowds. There is no need to go through the train station and waste time.
The National Gallery locker requires a 10 NOK coin. It is a long walk from the city hall tram 12 stop to the National Gallery. Try a closer station instead.
The discount on the Oslo Pass for cruise passengers is no longer available.
The information centre at the cruise terminal doesn't sell the Oslo Pass.
For the Folk Museum, consider visiting only the pink and red shaded buildings on the museum map + the stave church unless you're really interested in farm buildings. A lot of the buildings with staff in them are more souvenir shops than "artisan demonstrations".
Warnemunde:
Group transit tickets for Rostock are listed at the ticket machines under "single and collective tickets", the top-left button, not under "group tickets" (top-right button).
Talinn:
Pick up city maps at the TI behind the old town hall. They'll come in handy if you are walking to Kadriorg Park. The maps at the cruise terminal are not as good.
It is difficult to buy tram tickets. R Kiosks don't seem to sell SmartCards or transit tickets. Employees there speak limited English. They told us to buy tickets from the driver. We ended up walking to Kadriorg Park since it wasn't that far (25 minutes).
The Dome Church now costs Euro 1.50 for entry.
St. Petersburg:
Hermitage Museum:
A lot of rooms don't have numbers posted in easy-to-see spots, so pick up an official museum map if possible (they weren't available for us because we went with a tour group before the general opening time and the maps weren't put out till then).
The French impressionists are now in rooms 143-146, not upstairs.
Helsinki:
The newsstand at the Lansiterminaali terminal does not sell day passes (unlike what the guidebook says). Remain standing in line at the ticket machine outside. Only one machine at the tram stop accepts bills (thus the long lines), so bringing change may help you use the other machine, which takes coins, but not bills.
There is a typo on page 338: it is HSL ferries that go to Suomenlinna, not HKL ferries.
Nynashamn/Stockholm
Tendering ashore and getting to the Vasa Museum by public transit from the ship takes four hours. You may wish to consider Princess' shore excursions to jump the tender queue.