Well - just watched episode 501- love it when Dragon makes an appearance- hes so mysterious- and awesome :P
When he saves Luffy and Ace from Bluejam and his crew during the fire- in the manga it looked like a gust of wind but it was shown to be Haki in the episode- Bluejams crew fainted straight away - this is intriguing- cuz now we know he can definitely use this power
I believe we will see more of Dragon appearing as the series goes on cuz lately weve been seeing him more- just in short scenes or someone mentioning him- i think maybe after Luffy and the others have left Fishman Island- on the 3rd or 4th island into New World they will meet him- perhaps sooner???
I really cant wait for Luffy and Dragon to meet- but....its gonna be a long wait
Seeing as every series takes place on an island or place in the sea- 3-4 more series until we see him??? - thats.....a few years.... oh well- we'll get there soon enough :) - just have to be patient >.<