Small brown and red mushrooms generate far too frequently in swamps in the 1.8 snapshots, but only if the chunks are first generated at night. If you first generate the chunks in the swamp during the daytime, however, there will end up being the same amount of mushrooms there always were in previous versions (such as 1.7.4).
I have attached four screenshots of the same swamp: one loaded in 14w08a during the day, one loaded in 14w08a at night, another loaded in 1.7.5 at day, and finally a fourth generated in 1.7.5 during the night. As seen in the screenshots, the seed is "5716724006876013666" and the coordinates of the swamp are "x:-507 y:103 z:-1100".
As you can see, the 14w08a night swamp contains a much larger amount of mushrooms than the swamp from the same version explored during the day or the 1.7 swamps. Note also that the number of mushrooms in the 1.7 night-explored swamp does not differ from the number in the 1.7 day swamp. I firmly believe this is a bug and I hope it's fixed soon.
Note: The screenshots may appear in a different order than I listed them, so be sure to pay attention