I've done it many times, but it's not fun.
As was said, you have to have something with you to bang off the ice before departing (I have a small wooden "club") as all the water splashed onto the float during landing will have frozen. Watch out for a slippery float and be careful in your movements getting in/out.
As I fly an amphib, I have to make sure the nose wheel is free of ice as well and hope that it doesn't gather too much on the takeoff. I do a quick cycle of the gear after coming airborne to make sure that no ice forms where it shouldn't and that the nose wheel will travel.
As for de-icing the wings, using lake water usually works. Attach a rope to a 5-gallon bucket, climb up on the wings, lower the bucket into the water, pull up the water-laden bucket, pour onto wings, repeat. You have to make sure that it's not so cold that the water will refreeze (you could test this on the tail, for example). After getting the plane de-iced, be sure to check that all controls are free.
Also, check your water rudders. You might have a problem with them freezing in the up position after takeoff.
One other important thing, GREASE YOUR FLOATS. Get some grease (axel grease could work) and grease up your control cables that run to your water rudders at any place they go through a pulley. Slap it on thick and it should keep the ice off of those moving parts so your rudders won't freeze.