Do you use retina double size images or not in your webprojects. It looks good but the pageloading will be heavy. How do you think about this?
Like anything, it depends.
If the images are small (in dimensions) and illustrative in nature, they may compress just fine and not be much more of a download than the originals. Using sprites and such can help with all of that as well.
And with mobile, SVG is often a viable option.
For large images or photos, again, it would really depend on the particular project and particular audience. But yes, in general, it's nice to take advantage of the technology if it's there.