-- Last Updated: Oct-25-12 11:21 AM EST --
Like many others here, I started out in aluminum canoes and have a soft spot in my heart for them. And if you want a completely maintenance-free boat that is durable and can be sold for scrap metal (instead of taken to the landfill) when it reaches end of life, aluminum is unmatched.
But unless you are buying a boat that is going to sit out exposed to the elements all year, I think you would be happier looking around for a good deal on a used Royalex or composite boat. And if you aren't concerned about the weight, I would still prefer a polyethylene boat to aluminum. Even a slightly hogged or oil-canned Old Town Discovery will paddle at least as well, and probably better than a pristine aluminum hull.
For me, the disadvantages of aluminum just outweigh the virtues. Most have been chronicled here: heavy, very limited selection of hull shapes (none very efficient), hot as hades in summer, cold as a pump handle in winter, noisy as all get out, sticks like glue to rocks.
One disadvantage that hasn't been mentioned is the keel that all aluminum boats have. Nearly all aluminum canoes have a T keel with a fin that sticks down into the water. These are very undesirable in boats intended for river use. The T keel makes it even more likely that the boat will stick on rocks and ledges, makes lift overs more difficult, and resist turning the boat when you need to.
If you plan to paddle rivers, especially headwaters where you are likely to encounter deadfall, and you really want aluminum, I would look for a boat with a rounded "shoe keel" that is a little less onerous, but good luck finding one.