EDIT: Sometimes I see no increase in Sp. Att.
Like I had said before, sometimes it spaces out.
I fed all the ones I could in Feathers to a Pokemon I was training on Black and White and I didn't see any immediate change, but as I started to level it up, I saw some jumps in the stats that wouldn't have been done if I were raising it randomly.
It spaces out cause you won't get a level 1 with 60+ Special attack. The 62 bonus attacks are spread out evenly as it levels until it can't go up anymore.
It still goes up if you hit 100 because it just doesn't lock in your stats anymore.