If I had to do it over....
...I think I might've put the nested set data in a seperate table. This would help on the inserts/deletes by minimizing the amount of data to traverse.
One other side note: In my nested sets, I have different customers with unrelated trees. The nested set is keyed of the customer id first, meaning that the insert/delete operations for one customer do not have to effect all the data in the table. In effect, I have multiple roots in the table. Each root acts independently.
Not sure if it is similar, but I was thinking that in something like zIWTHEY, you could have each top level message be a seperate tree.
