Well, not on dvd burners, but i guess it applies the same way. as cfitz had clearly explained on the post above, buffer size does not make the burn quality better... it is just a matter of finishing the job fast, and without unnecessary linking caused by the burn-proof system. if your computer is not fast enough to provide the drive with the data it needs, then a bigger buffer is good for you, but it doesnt mean that a 2mb buffer won't do you any good... again, if your computer is quite fast, but then you do video editing, and stuff which takes too many pc resources, that would cause your drive too to use burn-proof... and a bigger buffer helps to lower the possibilities of that.
i have used both velocd 52x24x48x, which has 2mb buffer, and plextor premium 52x32x52x, which has 8mb of buffer, tested them on one same pc. they finished my test burn at almost the same time. plextor seemed to make a cleaner burn when i used the plextools q-check, but, very minimal differences. again, this could be media differences, but i used the same fuji 48x media. i chose to have the plextor because it rewrites faster than the velocd, and especially because IT IS A PLEXTOR. i don't usually do anything when i am burning something, probably surf a little, till a cd is done.