Yes I have heard that the ratings are overstated by the makers of the skimmer, but I would beleive that they are more accurate with your bigger name skimmers they would be a little more accurate. You can't compare a Seaclone with a Tunze or anything like that...but once again, I really don't know about the ones I mentioned if they are really that out of line with their suggested sizes. As far as the three I listed above their suggested ratings are:

ASM - 250 gallons
Octopus - 300 gallons
Tunze - 264 gallons