At the risk of boring others on here to death, all German nouns begin with a capital letter (I'm sure you know that really) and in the dative plural there's always an "n" on the end. For example "in 16 Tagen" Have fun in D!
Get a day rover ticket for the underground/tram/bus/boat. I think it was about 8 euros when we did it a few years back. Lets you travel all day on public transport including the boat so you can have a nice trip up the river, get off at the terminus (can't remember its name). Have a walk round there and then catch a boat back. Get the underground up to the Hamburg SV stadium and do a stadium tour.
Is it a good place to take your partner? Never been myself but a couple of my mates spent a few days there and it sounded absolutely mental, basically one big drink, drug and sex fest by the sounds of it!
There's a lot more to Hamburg than just the drink, drugs and sex. Same as places like Ibiza, beautiful island with a lot more to offer than just nightclubs.
It's good for both. Bit like Prague or Krakow where if you're there with a gang of lads on the piss you'll get pestered by beautiful women but if you're with the mrs, they'll disappear into the background and it's a different break altogether.