This was my 4th or 5th time at Zeeburg and I love the place. Some of the negative comments do need to be addressed however. Yes, it is very crowded in Summer, and yes lots of people will be smoking dope and partying late - but this is a city campsite and it's in Amsterdam, so what do you expect? If you want spacious marked pitches and lots of peace and quiet, it isn't for you and you should find somewhere further out of town. One reviewer called it "festival camping" which is a good description - if you LIKE that kind of atmosphere and don't mind a lack of space, this place is for you. It's a young crowd and a very chilled atmosphere.
As for the walk to the tram stop being too long or scary, the person who said "a half hour over a very long bridge" went the wrong way! From the 26 tram (Central Station to Zuiderzeeweg) walk through the long carpark and keep going along the edge of the lake with houseboats on one side and a hippy/traveller type camp on the other (If you do end up on a long road bridge over the water, keep going and descend at the next steps, but it's a longer hike). It may look a bit grim, but it's a nice neighbourhood, From the 7 or 14 tram (from Dam or Leidseplein to Flevopark), walk either side of the graffiti-covered overpass and take the steps over the bridge. Again, the graffiti (much of which is fantastic) may make this look like a rougher area than it really is - on either route, you will NOT get murdered!
I found the toilets very well maintained and were closed for cleaning several times a day (usually when I wanted to use them!). I've never come across people sleeping in them. The shower tokens may cost 2€, but last a long time - it's a pain that you can't switch them off as it's very diificult to dry yourself in a cramped cubicle until they stop running.
Breakfast is expensive however and the WiFi was still out odf action, but these are minor niggles. All in all, it's a great campsite if you want to live it up in the 'Dam for a few days, but be realistic abouit the clientelle and the noise.
Final tip: keep your food well stored as hedgehogs and ducks will get under your flysheet!