This all depends on where you live. Some areas have very clean power, but even then lightning can present problems. A fairly robust surge protector is a good investment—and this does not require a major expenditure. Both Belkin and APC make a wide range of various devices designed to protect home electronics. There are of course other reputable and reliable companies—these are two that I have used and found have good products a fair price.
I’d stay away from some of the very hyped brands such as Monster, not because they don’t have good products, but because they charge a premium price.
If you live in an area with significant power fluctuations or brownouts, buying a voltage regulator is probably worthwhile. And if you live where you get occasional power interruptions, you should consider a UPS for your home theater, just as you would for your computer. A combination UPS, voltage regulator, surge protector is not that expensive—just get one suitable for your needs. I have three different ones: computer equipment, bedroom TV, etc. and backroom TV, etc.
Even if you opt for a simple surge protector, make sure that it as connections for RG6 from your antenna, cable or satellite feed(s). Also if you have an unprotected phone line going into your system, protect that as well.