There actually was a working hydrogen fuel cell forklift at the last Promat show. Unfortunately it was at a small booth in a poor location at the show and I don't think too many people actually saw it. Over the last year or two I have talked with a couple of representatives from the fuel cell industry and neither were willing to say that hydrogen fuel cell technology will be cost competitive with current fuel options. It was obvious that they determined their strategies needed to be related to the clean burning properties and the ease of refueling (versus changing or charging batteries). Unfortunately, if it can't be competitive purely on fuel cost, I don't think the other benefits will be enough to make a significant change in the industry.
Also from a purely environmental standpoint, I think hydrogen fuel is not as "green" as many are led to believe. Though it burns clean, the processes used to create hydrogen fuel may not be. In some cases, fossil fuels will be used to create the hydrogen (or used to create the electricity that is used to create the hydrogen).
I'm not an expert on hydrogen fuel cells, so feel free to jump in and let me know if I am misunderstanding the process.