Keep in mind that if you want the recording to be of "DVD quality" you need to use either the one hour or two hour modes -- if all you want is VHS quality, the 4 hour mode would be similar to the VHS SP 2 hour speed. Recordings made at 6, 8, or 16 hours would be of very poor quality.
Another factor to keep in mind is that if you want your recorded DVD to play in most other DVD players, you have the best chance with the 1 or 2 hour recording modes. Due to the amount of compression needed to fit more video time on a DVD, you may experience some skips and stalls on some DVD players.
Personally, I never, if at all possible record more than two hours on a DVD (or 4 hours on the newer blank dual layered recordable DVDs) - after all, the main reason for DVD recorders is to record better quality video, not just longer video, and also have it compatible for play in other DVD players.
A commercial DVD can hold approximately 130 min of video information per layer. Most commercial DVDs have two layers at 130 min per layer, which is why it seems that the DVD is holding a lot more than two hours of information.
For more information on the actual labeling of DVD Recording modes, check out my article: DVD Record Modes - Recording Times For DVDs.
However, another issue that confuses consumers regarding how much you time you can fit on a DVD, involves the term "Disk Writing Speed". For a detailed explanation of the difference between DVD Recording Modes and Disc Writing Speed, check out my Quick Tip: DVD Recording Times and Disc Writing Speed - Important Facts.
Proceed to the next question: Can I create chapters and menus on the DVDs that I make using a DVD Recorder?