Temperature fluctuations
 

I've heard that fluctuations as subtle as 5 degrees during fermentation can affect the final beer quality.

With this in mind, I'm concerned about my ability to maintain a constant temperature for my batches. My apartment isn't very well insulated, so during the summer it gets hot during the day and cools off at night. The problem is even worse in winter as my apartment is heated by somewhat inefficient radiators.

So I suppose my question is...what can I do/what do other brewers do to ensure decent temperature consistency throughout the process. Am I being too concerned about this, or is it a real issue?

definitely a real issue.

I have my primaries sitting on a register for the summer months. This keeps them right at about 70F. I don't know if this would work for you or not.

Other methods, involve building a fermentation chiller, either a fridge/freezer with temp control, or a "son of a fermentation chiller". Search on both of those. Also, some people keep the fermenter in tub of water with a towel wrapped around it. Since water won't fluctuate so much during the day, it can keep the fermenter cool from the cooler air the night before.