whilst recursive queries are fun, as you can do a whole lot of lookups and join them together in one sql statement; they do take a long time to run, significantly degrading performance.
Take another look at the bits of the thread on using a nested set representation for hierarchical data. Flat structure, normalised data and fast queries. Some performance degradation on insertion, but since people usually read and update a lot more than they insert it's rarely an issue.
As for recursive queries - the old chestnut about premature optimization comes to mind. That and the fact that several databases have explicit support for hierarchical structures and appropriate optimisations to make access to those structures efficient - even if they set C.J. Date spinning in his grave ;-)
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