55 gallons of water wieghs about 440LBS, then you have to factor in the actual weight of the tank, gravel, and decor. Test it out with some sand bags or something.
I put a 29gallon on my desser and was worried about that, so I personally wouldnt do it with a 55.
I am sorry to all the people ahead of me for what I am about to say...
I find that most people are a little TOO reserved when it comes to ideas like this. You need to look at how the whole thing is supported, if the weight of the tank is able to distribute evenly over the whole of the dresser then you should be alright. The only time you really run into problems is when you place something heavy over a weak spot. I made this mistake once by putting a 40 breeder in the middle/back of a dinning room table, at 1/2 way it split the table in the center and dashed the tank. But with that said, I have never had a problem with the 30 sitting on a desk. As long as the furniture is level and sound structurally and can take some weight then you are fine.
If I build a dressing table or a set of draws then it WILL support any sensible size tank (or small dancing elephant) But a lot of cheaper furniture is just chipboard held together with a few tacks. It barely holds itself up
Sit on something, bounce around a bit... If it doesn't move or sag noticably, then it's probably fine. If it makes you feel like you shouldn't be sitting there, not a good place for a tank