So I know that Verbatim are the best media to burn with. But, my question is, if by using other brands am I going to increase my risk of burning coasters or far worse, increase my risk of getting banned on Live?

Thanks heaps.

You will not get banned from bad media. Coasters are your only issue

Thanks for that mate.

One more question (Promise ). Is it true that there's no need to check stealth with 1.4 (eg. scene released games) as the new firmware will simply not boot them if they aren't correctly stealth'd?

Well I would say might as well stealth check them to make sure everything is a ok and might as well not burn a game and find it doesn't work because it was badly stealthed or not stealthed at all. That is just my opinion.