Take a reasonably good 4:3 LCD monitor. Put electrical tape, or some other opaque tape, over the left/right/top/bottom 5% of your screen. Put scotch tape, or some other semi-transparent tape, over the next 3% of your screen. (So a total of 8% on all sides is covered.) Now do the same thing with a reasonably good 16:9 LCD monitor, but cover 5% on the left/right with scotch tape - so 8% on top/bottom, 10% on left/right.
You now have two serviceable approximations of crappy TVs - the very edges are completely covered, and some amount beyond that is visible but too blurry to contain text or other detailed graphics.
For extra credit, implement that effect in your rendering engine to save yourself some tape.
One myth I've heard repeatedly about overscan/safe areas is that HD TVs don't have them. That's not true. All HD CRTs have overscan areas and many LCD and plasma models do as well. Some don't but will simulate overscan for non-HDMI/DVI/VGA input, including HD Y'PbPr ("component") input. I suspect this myth exists because most people hook up their HDTVs using HDMI or VGA.
Another myth I've heard is that the title-safe area is a fixed size, e.g it's always 2cm from the edge, or it's always 50 pixels from the edge, so it's proportionately smaller on large or HD TVs. That is also not true. Safe areas are generally proportional to the TV size, and that size is fixed regardless of the resolution the screen is displaying - they're a physical property of the TV screen, or simulated as such. I suspect this myth exists because higher-end and newer HDTVs do have smaller unsafe areas.