If you mean "horizontal shear", where the layers of wood slide over one another at a bearing point, then yes, you should consider the published values. This type of failure will always occur before a tearing across the grain itself, for which there are usually no published values, at least in US practice.
In the Australian code the values given for E, the elastic modulus, include an allowance for shear deformation. If you only want it to calculate deflections that should be enough.
What do you want to know for?
I'm pretty sure that the 'Encyclopedia of Wood' by Stirling Publications has Shear Modulii for various species; will check my book tomorrow and let you know.
The shear modulus G in timber design in the UK (to BS:5268) is taken to be E/16.
The central deflection due to shear on a beam from a UDL is calcualted using
wL*2/(8AG) then multiplying by a form factor, C (1.2 for a rectangular section) this is then added to the deflection due to bending.
As you can see, there's quite a mix. 'l' is short for longitudinal, 'r' for radial and 't' for tangential Glr is the modulus for the 'longitudinal-radial' plane. If you need the tabular information, I can scan it and email it to you.
Taro:
Wood, being orthotropic, has 6 values for poissons ratio. Doug fir for example has values 0.29, 0.45, 0.39, 0.37, 0.04 and 0.03 for Ulr, Ult, Urt, Utr, Url and Utl, respectively.