Fat loss is as permanent as it would be on any diet/supplement regimen - obviously if you eat like a pig, the fat is going to come back. Off the top of my head, the only other way to get a "rebound fat" effect after ceasing DNP, is if you did it high dose for a long time without the proper supplementation, and burned out your thyroid. Those with more bug spray wisdom than I, please correct me if I'm wrong.
I can't speak for everyone who's used it, but for me, the results were amazing in a short period of time. Suffer for a month dieting those last few pounds off the old fashioned way, or suffer for a week on DNP? Tough choice. Can't argue with striations. It's not something I personally want to get into the habit of using often, for the lack of research on longterm delterious effects, but a little once in awhile to carve off those last hard-to-lose pounds is totally worth the yellow sweat and lethargy.
If you're planning on experimenting with DNP, do as much research as you possibly can before popping the first cap. The search function is amazingly helpful, and we've got great people on these boards who can answer pretty much any question you might have about it.