With the introduction of FBX import (to IMVU) its likely user generated content will need some degree of re-scaling for proper use in IMVU. For Blender users, without re-scaling or resizing, imported assets are much larger than necessary.
Addressing this disparity can be done in three ways; adjusting scale at export; adjusting scale at import; or adjusting the units of measurement in Blender to compensate, essentially allowing a 1:1 transfer between programs.
Assuming use of available example or starter files. To adjust on export; in Blender work as normal then during export to FBX from "File", "Export", "FBX" ("File » Export » FBX (.fbx)"), under "Main" set the "Scale" value to "0.01" then export as normal ("Export FBX" top right). The resulting FBX file can then be imported using IMVU's default scaling value ("Apply scaling:1.0").
To adjust on IMVU import; in Blender work as normal and export leaving the "Scale" unchanged. In IMVU once the file is loaded, change scaling ("Apply scaling") to "0.01" and import.
To compensate using units; in Blender access "Scene" properties and in the "Units" subsection change "Length" to "Metric", type "0.01" in "Unit Scale" input box, then export from Blender and import to IMVU using the default scale values.
In each case the result will be correctly sized content, meshes, skeleton, animations and morphs.