This stores the version of the driver. The numbers you might see are all over the place. 
For example the Active Directory driver is still 3.5.x even the version in IDM 4 (latest as I write this is 3.5.13). Which is actually a good thing as they use the same driver shim (addriver.dll) for IDM 3.5, 3.6, and 4.0 instances and the licensing credential does not change either.
The User Application drivers usually show a very different version number. For example an IDM 3.5 Provisioning module User Application driver shows a version of 0.20080709.164851. Other drivers like eDirectory or Loopback, show in the format of 126.96.36.19949 as an example.
Usually I just look at the trace, and events on the Subscriber channel will have an XML attribute called version in the <nds> node, whereas events on the Publisher channel will show the shim version.
More Information#There might be more information for this subject on one of the following:
[#1] - http://www.novell.com/communities/node/12528/what-do-various-idm-driver-object-attributes-represent-part-3