This posting will probably not increase my popularity..... I apologize in advance! :)
I would like to suggest to re-organize the subject tree according to MSC (www.ams.org/msc), with a layer above the first two digits (which is implicit in MSC anyway). Reasons:
* Everybody knows MSC, thus the subject tree would be more easy to browse for the occasional garden visitor.
* This would make the slant towards discrete math (now: 3 out of 10 top level categories) less obvious and encourage
non-discrete people to submit their problems.