It seems to vary by species, but it's usually a short time, especially if they're not refrigerated...on the order of several months. The longest I remember was someone on the forum who said he/she got germination after three years. That would be highly unusual in my opinion.

I know that humidity also plays a big part too. Has anyone put bamboo seeds in the freezer?

I have some Moso seed that I purchased in March 2005 that I refrigerated to test germination longevity. I will be sowing soe of it this week.

No I have not frozen them.

well I think Kudzu is talking about me, I can say that after 3 years of no special care in storage some of the seeds of D. strictus and D. Callostachyus germinated in about a week and now I have 20 seedlings of 8" long, those were from a bunch of 100 of each one, but none of my maybe 100 seeds of moso germinated, so maybe I was lucky or maybe those Dendros have a long viability and moso seeds didnt.

Have a look at the RHS seedbank database (http://www.kew.org/data/sid/). They are currently attempting to collect and store as many of the worlds species as they can. Their database currently only appears to hold info on some Bambusa species e.g. the following was taken from one of the B. arundinacea (syn. bambos) entries:

Storage Conditions: MCS= 26% (Thapliyal et al., 1991) Rapid loss in viability with seeds stored at ambient temperature (Dent, 1948); viability lost within 6 months hermetic storage at room temperature with 13±2% mc (Kaul, 1979); seeds tolerate desiccation to 6.6% mc (Thapliyal et al., 1991)

You should also be able to find information on storage/germination conditions on the following link

Here is a link that might be useful: Seed dormancy

I still have MOSO seeds in the freezer; they are keeped at +41F;I have fresh seeds(2 month old) and old seeds(2 years old); I can tell you that the old seeds are still viable and the germination rate is about 7-10%; the fresh seeds have a 35% germination rate; every 2-3 month I make some trials with 100 seeds, and in this way I know the viability of the seeds;the most important thing is the constant temperature and the humidity of the seeds

Ocium Nate and Puiugrosu, you both mention humidity as a contributing factor regarding viability of seeds. Is high humidity good or bad for seeds?

Humidity speeds the death of seeds. As a general rule seeds should be kept at the sum of relative humidity and temperature (F) under 100. For example if the relative humidity was 25% then the temperature would need to be 75 F or less. Cooler and drier are better unless the seed is "recalcitrant" or has a high moisture content if the seed has a high moisture content freezing the seed will cause ice crystals to form and cause damage to the seed.

Thanks ociumum nate!