This was originally sent to the RPO at Model Railroader magazine, but as they haven't published it (giving them several issues' time to do so...) I figure it's fair game to repost it here.
In part 3 of Dick Christianson's excellent series on the Salt Lake Route (March 2010 MR) the author shows the blue plastic tool, describing it as a way to pull Unitrack joiners out of their sockets (Fig 4).
At least for N-scalers, that's not the only thing that handy bit of plastic is for. As it turns out, it's also a track gauge and right-of-way profile tool, as the illustration below shows; the upper portion of the tool shows limits to pantographs and other overhead gear (it's not clear whether it would apply to larger US equipment, like double-stacks, etc. though.)
|Shown: F7a Superchief, and a JR East EF81 in Cassiopeia livery, on a T-Trak module.|
Further, it would appear that the placement of the joiner-pulling opening is not entirely arbitrary. At least for Japanese rolling stock, it serves as a coupler height gauge as well.
Finally, in Figure 8, Mr. Christianson uses a paper template to measure track spacing. As it happens, that other blue plastic tool from Kato, the rerailer, has notches on one side to help you align up to 3 tracks at 33mm centers, to help do the same thing.
Pretty handy little Unitrack multi-taskers.