I just changed the 2-lamp T-8 ballasts in one of the shop lights over my bench for the second time in probably five or six years as well. Like the OPís, it also gets a lot of use.
I remember back when the T-8 electronic ballasts first came out, they would frequently burn out sometimes only within a year or two. Those GE Triad ballasts come to mind.
To me anyway, the newer ones made in the last few years seem better as far as life span goes, but IMO, they still donít last anywhere near as long as the old potted magnetic ballasts used to.