1) you have to have an on-camera flash to trigger the off camera flash - the problem is when you don't want an on-camera flash to be firing. Sure you can set it down to it's lowest setting, but you are still introducing a front light source.
2) you have to make sure the infrared receiver on the off-camera flash is 'visible' to the on-camera flash. This limits your range and makes using that flash more complicated and less reliable.
So, I was at my cousins wedding and her photographer was using the Cactus Triggers, which are one of the least expensive triggers on the market. I had read about these, but had heard mixed reviews on their reliability. But this photographer had nothing but good to say about them.
I looked more into them and they had some problems with one of the versions (v4). Now they have the v5's. So I ordered a pair and have been trying them out.
Overall, I really like them. This is not a review of these wireless triggers per se, so I won't elaborate too much. Briefly: they work on manual setting, so you don't get to use Nikon's TTL technology (which is basically Auto Flash mode). They are very reliable thus far. And I love not having to line up the old infra-red sensors. The only problem I have found thus far is that they didn't work with my SB-600 flashes until I put some duct tape covering one of the pins on the bottom of the SB-600s. Thanks flickr.com forums for pointing me that direction.The newer triggers are nice because they claim to work up to 1/1000 shutter speed. They worked at 1/500 for me, but not so well at 1/1000. Further testing may reveal otherwise.
One more shot: settings: 70mm ISO 800 f4, 1/125 -off-camera flash powered at 1/128 M (SB800)
By the way, here was my set-up for this shot.
And don't worry, the goblet is empty.
Pic of the Day:
Picture came from the photographer, Amanda, who was so kind to entertain my questions regarding the cactus triggers... I think she really nails this shot: great evening light with equally subdued pose and colors; great contrast with her depth of focus, and superb lines/curves take me through the whole of the subjects. I don't think she uses any reflectors, diffusers, or fill flash... just good natural lighting.