how many people run this card? with the new red-eyes structure do yall think it will come back into play? at least in side decks?

Basically, no one really runs this card because it's not really needed, even against a Dragon deck.

Dragon's Roar won't make it any difference because of stuff like Tribe Infecting Virus, Rivalry of the Warlords and other type designating stuff. Dragon Capture Jar isn't that good because

1. It only switches them into DEF

2. It's continuous so it's a waste of m/t space

3. doesn't destroy them

4. Unless you're up against a hardcore dragon deck, it won't be that helpful.

I doubt it'll see much play even in side decks.

Dragon Capture Jar isn't that great a card, even in the Side Deck. Like HalfDemonInuyas said, it only switches Dragons to DEF, and besides, even Dragon's Roar includes 3 Stamping Destructions, which laugh in the face of things like DCJ, Rivalry etc.

I have a question concerning the ruling of the DCJ card. I know that it is continuous, but does it mean that every dragon i summon after the Jar is activated is affected? and if so, does it mean that my card has to be summonded face up, or can i set it in face down defense?

If you summon it face up ATK, it will be switched into DEF position after it hits the field.

You can still set dragons in f/d DEF position.