"Niek Otten" wrote in message
I've also read about some other non-event methods,
I haven't used them and forgotten what they are.

One I remember (and just tested to be sure) is that you can change
the comments of a cell from within a function.

Oh yes, that was one.

I know there are a few more but I can't remember those.

Vaguely recall reading some way an xll type UDF can change the interface
too, not sure.

I do think these should be considered bugs so they might be
gone in a future release (the one I tested is still present in 2007)

Well, there's good bacteria and there's bad bacteria !

Another FWIW, normally format changes don't trigger a calculation so UDF's
can't respond until the next full calc. But again there are ways, eg define
a named formula using the xl4Macro Get.Cell function with format type
number, add (Now() * 0) to the result to help it update when used in the
UDF.

Regards,
Peter T