Just noticed this thread. Here are a few things that may help address some of the issues raised by several folks earlier in the thread.
1) If you are having trouble keeping your fermentation temps down, a good trick is to place the carboy/bucket in a big trough of water, and drape a t-shirt over it. The t-shirt will soak up the water like a wick, and the evaporation will cool the fermenter down by a good 5-10 degrees F. Blow a fan on it and add ice to the water and you get an even bigger drop in temp.
2) During high krausen (the most active point of fermentation when the yeast are bubbling away like crazy), the internal temperature of the beer can often exceed ambient temperature by up to 10 degrees F. This can be enough to produce excessive fruity esters or worse, harsh, solventy tasting fusel alchohols.
3) If you are doing higher gravity (> 1.060) or very hoppy beers, you will lose hop bitterness if do partial boils.
Hop alpha acids have a harder time "dissolving" into a wort the higher SG of that wort becomes. Adding all of your extract at the beginning of a partial boil will essentially create a wort that has about 2x the OG of a full sized boil. This causes the hops to saturate the solution. Think back to junior high school science class when you dissolved sugar into water, eventually no more sugar will dissolve. Similarly, you will not get all the bitterness that those hops can provide in a more dilute wort.
The solution to this is to do what's called the "extract late" method. You add about 1/2 to 1/3 of your extract up front, do your partial boil with all the hops added at the proper times, and then add the remainder of the extract with about 5 or 10 mins or so left in the boil (just long enough to pasteurize it). This also helps reduce something we Beer Judges call "extract twang", which is an off flavor caused by concentrated boiling of malt extract. It also helps if you want to brew an extract Pilsner or Kolsch (or other light colored beer) because it doesn't undergo as much Mailliard reaction due to the lower sugar content, keeping the color lighter.
4) When topping off partial boils to full volume, be sure to use boiled water so that you are not allowing any bacteria or wild yeasts to inhabit your wort. Additionally, if you use city water, there are 2 forms of chlorine that the city sanitation folks add to keep the water clean: Regular chlorine, which will come out in a boil or using a basic household charcoal filter, and chloramine, which will not come out in either the boil or will come out in a charcoal filter only if you are exceedingly patient and allow a very slow stream to fill your brew pot. You can purchase Campden tablets to treat both types of chlorinated water. Each aspirin sized tablet is enough to treat 20 gallons of water. Split up one tablet (for 5 gallons, you only need 1/4 tablet) and crush it up before adding it to your water. Chlorine problem solved. (Chlorine in the water is the leading cause of chlorophenolic off flavors, which taste like band-aids or chloraseptic). I find this to be the #1 most common flaw I come across in competitions, especially for new brewers.