GD Star Rating adds 2-3 MB on RAM usage depending on the features you use. With all plugins features active it uses 3.1MB. So far there were few reports of strange memory usage, but so far I couldn't confirm any of them as related directly to GD Star Rating. In two reports, problem turned out to be the theme with badly formed loops usage that made hundreds of unnecessary calls for post content, triggering rating rendering that lead to memory increase. Also, one report was caused by PHP 4.4.0. But both of them caused plugin to use 5 or 6 MB more than it should be.
I am using plugin on all my websites, and on some 20 websites of various clients, located on different hosting servers, and so far I had no memory related problems.
If you can provide me with errors causing the memory increase (not message about increase, but rather underlying error) I may be able to see if there is something to be done. But right now some 30.000 blogs use the plugin, and only handful of such reports point to some non-plugin related source of the problem. Also, problem can be caused by some combination of other plugins and GD Star Rating.
Regards,
Milan