Good advice here so far. I worked for Tweeter, Etc. for a number of years (mostly when they were financially healthy so...) I sold more TV's than I can count. A few things.
1. You can not truly calibrate
your TV to your eye or a friends setting. Calibration, like setting the levels when you record are dependent on the particulars of the source and the room. If your room, during the time you do most of your viewing, is very bright or dark it will change the optimal setting of your set.
2. This doesn't mean setting your TV to your eye is useless, of course. TVs are shipped set so they catch a potential customer's eye in a showroom setting (read: screaming bright). It is
better to take it down a good deal even without proper calibration. The issue is twofold. The first problem is that our eye has no consistent mechanism to adjust settings accurately for the scaler. While we can see some amount of line crawl and such with a normal picture, you do really need black and white patterns
to make the proper adjustments. Secondly, we are so accustomed to TV pictures that are really too bright. Therefore, unless you are very accustomed to seeing a properly calibrated set, most everyone setting their TV to their eye will make their picture much brighter than it would be if properly calibrated.
3. I haven't looked to see what calibration DVDs and kits are out there today but, in addition to the test pattern such as the one shown in the link in issue #2, you need color filters to properly set your levels. These filters look like a color "gel" that is used in stage lighting (i.e. a colored piece of thin plastic). A good kit will typically have at least a red and a blue color filter. If the kit does not have this it isn't useless, it is just useless for color calibration. Having the pattern to set your TV's scaler is better than nothing, it just isn't the whole job.
Hope this helps somewhat.