I can barely count to 99 ....... no hope of remembering what is on them all ......... shoot I have only just moved to four and cannot keep track of them! ........ 99! Arghhhhhhhhhhh!!!!!!!
Throughout more than two years of near-constant usage, I have discovered that the optimal pattern of operation of a full KDE desktop environment on an original model 4G or 701 EeePC is to ensure that apps are set to open with the 'Maximised' and 'No Border' window settings forced, and to run one such app per desktop, utilising the Ctrl+Alt+Arrowkeys to navigate between them in an instant. Since GKrellM does not conform to the standard KDE window control method, I usually set it to autorun upon startup and thus always open on desktop 1 - thereby leaving 'room' for nineteen other apps. I have accordingly since found (while at work, generally) that with even that number, I do occasionally still run out of desktops nevertheless.
Furthermore, I have found that this pattern of usage has by now become a firmly-entrenched habit - because it is such a convenient and efficient method of desktop utilisation, I have by now become not only accustomed but also pretty much entirely dependent upon having so many desktops. I believe that the reason for this bears heavily upon your comment of being able to remember where apps are, because with this method such memory becomes more spatial in nature, rather than abstract - because a peripheral glance at the pager indicates one's present position, in the overall 'map' of desktops. As I am male in gender, I find this 'locational' memory seems more intuitive to me somehow, and so I am able to flick between apps surely, and with ease.
For that reason alone, I now detest using Windows - I feel very claustrophobic, when requested to do so, and I also feel lost and clumsy, as my fingers instinctively keep hitting the Ctrl+Alt+Arrowkeys. There are certainly plenty of other reasons to detest Windows, but that one in particular is always the first thing that rankles - with the lack of any Klipper usually being the next. ;-)