I run out of permanent slots all the time with my rainbow FG farmer deck. 6 shard of gratitude, 6 hourglass, 2 mindgate, plus quantum towers, as well as a few cards like sanctuary or anything I might happen to steal.
I still think that the number of slots is about right; otherwise it would be unbalanced. For the record, I have pulverized my own stuff to free up space for something better :p
