Seems to me there are two rather different usages here
a) an alert within the normal UI, to let you know something odd happened
b) a diagnostic when debugging where you need a 'bigger' alert.

For b) a 100mS simple delay is probably perfectly fine. I've done debugging where it would be really nice for there to be a good way of 'interrupting the delay' to get in to the problem process; an associated visual widget to click on or something.

For a) a delay that holds up everything is not a good idea. Some form of alarm (like the morphicalarm is supposed to be) that keeps the UI moving is going to be least annoying. I think it's likely that there are better feedback concepts than simply flashing the morph. 

tim
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tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
A paperless office has about as likely as a paperless bathroom.