I'm facing the same problem with other modules, but rather than end users, its me, being lazy, and not having to resize 100+ pictures.
Image Magick and some simple bourne shell scripting, allows you to easily resize a bunch o images. no problems. 1/2 an hour of scripting, and the script is re-useable.
Damned windows users.
I see some new svn add/updates recently for the ImageUpload module which looks promising, shouldnt be too hard to take some of the functionality from this module to be used elsewhere, provided you know what your doing

Sure, this could be coded into the image manager or whatever other modules, but then there are problems with php memory limits, file size limits and other limits on mycheaphost.com etc. it's better to resize the images before you upload.