Car audio has been a hobby of mine for 15-20yrs now, and to this day I have never seen an industry that even comes close to the amount of myths and misconceptions that exist in mobile electronics.
Almost all of us here love a great sounding system and because you're here on this forum now, most likely you will purchase and install the components yourself.
Or maybe you just want to make good informed decisions when buying equipment. (Heck maybe you just get your kicks n giggles by trolling the A/V forums)
Caution: I'm hopping up on my soapbox now.
I have found the following video to be worth MONTHS upon MONTHS of sifting through the entire interwebs (including videos, forums, websites, best friends, exchange students, dark alley capacitor salesman, etc) for the truth about mobile audio.
Seriously, the following video presented by JL Audio in Daytona Beach, FL (spring 2011) is an absolute must.
You have to watch it NOW! (or at least before doing any audio system upgrades)
The video itself is directed mainly at stereo shop owners but the information applies to all.
I wish I could stress even more on just how enlightening and empowering this video is, but alas all I can do is provide the link and these instructions:

Step1: Grab a drink and some snacks
Step 2: Get a pencil/pen and some paper (they came before computers, just google it)
Step 3: Note important information and the time it took place in the video...

'cause 3hr37min of time well spent is available by clicking the link/video!