how good are burnt dvd's?

I have a couple buddys of mine that are burning a bunch of dvd's for there own collection. They are always asking me if i want any or want to borrow them. My question is are they just as good as store bought ones or even dvd's I get from Netflix? Is the audio quality the same? video quality? Is it noticable? If its not recorded the right way, could it hurt my system? Speakers etc? I would just hate to spend all my time and money trying to build the perfect system, only to cheap out in the end. thanks for your help.
It's all 1's and 0's. I can't tell the difference,
especially the audio tracks. A copy of DTS is still
Not as good as medium-rare DVD's, the burnt ones just give me heartburn. Medium rare with some A1 steaksauce, forgeddaboutit!!!!!!
Now my non-smartass reply
If done correctly they should be an identical copy of the origional, only difference being the striped down look, which can be overcome by a good printer.

Im sure that not all DVD discs are created equal, and im sure they go for the cheapest quality they can find when burning DVD's however, im sure that the production companys skimp out where possible to increase revenue, so i would say equal.
I like Taiyo-Yudens. Work great for porn and can copy even those extra-sooty DVDs.
you have to consider the individual movie per se. there are programs available for dvd ripping (ie...dvd shrink, dvd decrypter, and so on). that being said, the majority of major releases are on dvd-9 dics. however, dvd-r are a dvd-5. the difference?? dvd-9 is 9+ gb while dvd-5 is 4.7 gb. hence, you must shrink the movie to fit to fit it on the dvd-5. the best way to do this is to completely strip out all the menus, special features, subtitles, and different audio languages. really, have you ever watched lord of the rings in portuguese? back up quality of 70% or more is pretty indistinguishable from the original. i've seen backups that were about 55% of the original. not too bad, but some scenes were a bit overly pixelated. i'll agree with gunbei....taiyo yuden discs are amongst the best available. check forums for further info on backing up your dvds.
Well, you may go to jail or get a HUGE fine...don't tell everyone what you are doing?

It depends if they're DOWNLOADING movies and burning them. Are they ripping the DVD and compressing it into some DiVX or MPEG format then reburning it? It's probably likely that it's a DIRECT COPY burn just like on CDs. Quality... you won't be able to tell the difference if so. If it's downloaded, yes but the quality is QUITE impressive if it's a 700-1.5 gig MPG/DIVX compressed movie. The more you compress/change formats the lesser the quality will be. This also takes a long time. Chances are, they're doing direct copies.
Basically what Kgturner said. But whether you can tell a difference or not would be entirely subjective. If the movie itself fits perfectly into a single-sided DVD-R then it should be the same. But theoretically, if your compression rate is 90% of the original, it can't possibly be the same as the original. Many blockbuster action films tend to be bigger in size and if you like the movie, they'll be worth buying.