Update: See note at the end, that’s good news; kind of.
I have been a fan of NextGEN Gallery, a plugin to WordPress to manage image assets, since it came into the scene. It is easy to use, capable of interfacing with different presentation styles, until recently well-supported. It has many users and deservedly so. However, I would like to alert all users of NextGEN Gallery that its file uploading inflates the file size for some reason. Click on the opening image and take a look at the local file sizes on the left and compare them to the Web site gallery file sizes. You will see a huge bloat. I posted a problem report on WordPress forums where NextGEN used to get support but as of today there was no answer. I also reported this to NextGEN on their Google + account, no movement there either. They only suggested that they do not support the users of the free version and that I may report it on their bug report site. I reported the problem as they suggested, and reminded them that although the plugin was free, I made two donations to Alex Rabe who graciously accepted them. These inquiries have not produced any result either. Feel free to compare your local and server file sizes and report your findings as comments to this post. Perhaps with more information they can get to the bottom of it sooner.
I am concerned over this not from a space utilization view, but content delivery perspective. I have unlimited storage quota where I host this site. But when the system has to deliver a 1.1 MB file instead of a 480KB file, the delays are inevitable. Yes, the difference will not be huge, but when a gallery contains 30-50 images the toll on the page load speed will be significant.
I am also not suggesting that you should worry about your site until you lose sleep over it. But do worry about the future of NextGEN Gallery as the new owners at Photocrati do not seem to be as responsive to user reports as the solo developer Alex Rabe used to be. Let us hope that Photocrati will have a change of heart and start listening to bug reports.
Note: After Dennis reported that he did not experience this problem and the file sizes were the same on local and remote, I tested a couple of things. First, I disabled the Flash upload and uploaded a file. The file size remained the same, good! Then I enabled the Flash upload and uploaded the same file once more, and the file size remained the same, good but question. I have a duplicate copy of the file in the same folder since NG tries to maintain the gallery integrity and they are dimensionally the same but file sizes are vastly different. The disable-enable Flash seems to have done a kind of Heimlich maneuver to dislodge whatever was causing this problem. The question remains though, how to make sure this does not happen again.