I always interpret the term "J-Horror" to mean Asian vengeful ghost horror, whether it be from Japan or not: Ringu, Ju-On/the Grudge, Kairo/Pulse, The Eye, Shutter, Dark Water, etc. Even Takashi Miike joined the party with One Missed Call, which both contributed to the genre, and satirized its over-saturation by going beyond the normal gore standard for the subgenre. Yes, this subgenre was in decline a while ago, and is essentially dead at the moment.
However Asian horror in general is by no means in decline. The more popular trend now is gritty, gory revenge thrillers like, as Straker mentioned, the Park Chan Wook trilogy, of which Oldboy now has an American remake (expect more!), The Chaser, Bedevilled, No Mercy, I Saw the Devil. And "Asian Horror" is no longer pigeonholed as vengeful ghost films because there's all kind of variety. Kimo and Timo's death cult themed short is the best segment on either V/H/S movie, hands down, and their redneck slasher Macabre us a most-see for gorehounds. As has already been mentioned, The Thirst (vampire) and The Host (giant monster), and a film like Three...Extremes shows the variety coming from Asian directors, none of which being vengeful ghost.
So -- I haven't answered the poll yet because I'd have to ask V, what do you mean by J-Horror?
- another name for the Asian vengeful ghost genre
- any Japanese horror
- any Asian horror