I do it similarly to gatz--I have a "LJ Icons" folder, then subfolders for either the topic, or the icon-maker. For instance, I have a lot of icons by girlyb_icons, so she gets her own folder, then I subdivide that by topic.
Otherwise, I divide the topic folders by icon maker, if there's a lot, or the miscellaneous ones just lie about at the bottom of the topic folder until I notice that I have a few by a single maker. Since I can see the icon by viewing by 'thumbnails', I don't usually bother to label it by what it is, but rather by who to credit.
As far as 'rotation'...the only ones I typically rotate are the seasonal ones, most of which are my girlyb icons. The others, I just do as it suits me. I do have a folder labeled 'my used LJ icons', so I know what I've actually used before, but I rarely even open it again. When I delete an icon, I just recopy from LJ to that folder. (This crazy step is also because I have three computers, and not all my icons are on all my computers---so I never know where stuff has come from.)
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Otherwise, I divide the topic folders by icon maker, if there's a lot, or the miscellaneous ones just lie about at the bottom of the topic folder until I notice that I have a few by a single maker. Since I can see the icon by viewing by 'thumbnails', I don't usually bother to label it by what it is, but rather by who to credit.
As far as 'rotation'...the only ones I typically rotate are the seasonal ones, most of which are my girlyb icons. The others, I just do as it suits me. I do have a folder labeled 'my used LJ icons', so I know what I've actually used before, but I rarely even open it again. When I delete an icon, I just recopy from LJ to that folder. (This crazy step is also because I have three computers, and not all my icons are on all my computers---so I never know where stuff has come from.)