I have a little update on these ishoot triggers. Like I say, I bought the ones with receivers that have a hotshoe (well, two each actually) and then a 3.5mm jack. The instruction manual says something like "1/500s sync speed (depends on camera)." I tested where the cutoff is for my D90, and it looks like the best you can do is about 1/160s—anything faster and you get catch the shutter half open with the flash. Switching to rear curtain sync didn't change anything, either (does that only control the in-camera flash?).
I thought it might be a delay in my studio lights (alien bees B400), so I tried firing an SB-600 set to manual on the ishoot's hotshoe and got exactly the same results.
This isn't a limitation for me since I won't need shutter speeds faster than that, but I thought I'd share just in case anyone is planning on using these things to overpower sunlight or something. These are great little triggers!