I have to say that this is a strange problem. A dot big enough to be visible to the naked eye seems strange, because the laser is hitting an area that is microscopic. So one single failure of the laser is not going to produce that big of a dot. Multiple failures of the laser would certainly cover more area, but how coincidental would it be for all of those failure just happen to form a perfectly round circle on the disc? It would, for one, mean that the failure is occurring at the same vicinity in a revolution.
So these dots make me think that either something really catastrophic happened (perhaps a biiiiiiiiiiiiiig overpower of the laser, big enough to bleed from a microscopic point to a sizeable area easily visible to the naked eye?) or that the disc has problems and that there are splotches on the disc where the dye seems to be problematic.
My best guess is that this is a problem with the media and that there are just bad spots. When I was burning my TY +Rs at 8x, I encountered the same problem with little splotches–perfectly round and pretty big (several mm in diameter). What was interesting was that one of these splotches straddled a 8x->4x downshift (the drive slowed down the burn at the end). The part that landed in the 4x region was barely visible, and if it weren’t for the sharp contrast of a splotch that got cut off by the downshift, I would not have noticed it. So my theory (I must emphasize, this is all just my best educated guess based on what appears to me to be likely and unlikely scenarios) is that the 4x strat was able to better cope with these problems on the disc. So I did a test; I changed the write strat from a T01-00 to a T01-01 strat, burned another disc at 8x, and the splotch as there, but not nearly as pronounced, and the error spike from it was, well, almost non-existant.
My (educated-guess) conclusion: it’s a problem with the disc, not with the laser. And with the proper write strategy, this disc defect can be better coped with.