Nope limit on the number of games. I was behind someone who traded in their gamecube with 14 PO titles and got a bonus $70 in credit. So I assume that the 6th, 7th, 8th, so on ...
Each get an additional $5 each. The store was swamped because of the new trade in deal. They told me that they started telling people on Friday night, and in the first 30 minutes on Sunday did got over $300 in games traded in. I believe them. They PS2 and Gamecube games laying all over the counter.