Its pretty likely we'll be DP-On from September! 4 sets - HP, CG, DF, PK. That's a normal rotation. This makes waiting for the set after Great Encounters a better bet. Don't buy too many Diamond&Pearl/DP1 packs - there's nothing that special in it. In fact, its rarely a good idea to buy loads of packs from just one set. You can play pretty cheaply if you want; trainers can be tricky but you can usually trade them from kids who don't want them.
HP, CG, DF, PK til September 08
DP, MT, SW, GE til September 09
xx, xx, xx, xx til September 10
Its not rocket science! Four sets in, four sets out.
MG