Good thing this is rubber side down and I can totally dissagree with Serowbot.
If the carb is clean, you use fresh gas, and ride every week, he is correct. However, if you let it sit up, especially if it is 10% ethanol, crud starts to build.
There are two fuel additives I consider very good, and both work differently.
Techron - This is a high concentrate detergent. It cleans very well, but does not suspend much. Good for some hard clogs. Add too much, and you get nothing, as it has no energy itself.
SeaFoam - This is like magic pixie juice! An amazing solvent, and it has some energy. You can actually (kinda) run the engine off it with no gas at all. (It will stumble and stall, and that is if it is not in gear) Also, it seems to be very stable, especially with 10% ethanol fuels.
If you get on the MIG forum, you will see lots of folks singing the praises of seafoam. One use that I can personally say works is when you have badly gummed up carbs with occasionally sticking floats. Get it running with gas, than (using a diner catchup bottle or something) fill the carb with pure seafoam. You will have to work to keep it running, and after a short time, let it die. Let the seafoam sit overnight, and the next day, drain the bowl and start it up on gas. After a few seconds it will clear out and WOW! I have put up to a quarter can (3x the recommended amount) in a tank on my Marauder and ran it through. On the next tank of clean gas, you could feel the difference. (I used to travel for work and my bike might sit up for a month or two)