TITLE: What's so great about blackboards?
QUESTION [40 upvotes]: Many mathematicians seem to think that the only way to give a mathematics talk is by using chalk on a blackboard.  To some, even using a whiteboard is heresy.  And we Don't Talk About Computers.
I'd like to know people's opinions on this.  In a - probably useless - attempt to forestall a flame war, let me try to narrow down the question a little.

I'm interested primarily in the effect that the medium has on the talk.  This will make comparisons difficult since saying "X gave a rubbish talk using a computer" leaves open the possibility that X would have given an even worse talk using a blackboard.  So please try to analyse why you have a preferred medium for presentations.  This isn't meant to be a collection of tips for making good presentations (though I can see the value in that).
It may be just my impression, but it seems that this attitude is peculiar to mathematicians.  Is this true, in your opinion?  Is there something special about mathematics that makes it so right for blackboard talks?
I'm interested in opinions both as speakers and listeners.  Your answers are allowed to be different from the different perspectives!
It may be that the type of talk has a bearing on the medium.  Try to take this into account as well.
I'm possibly completely out of date on this - maybe everyone has now fully Embraced Their Inner Beamer.
Please be nice.  By all means, praise good behaviour ("X gave a really nice talk using a combination of rope, blancmange, and a small aubergine; it wouldn't have worked so well with only chalk") but let bad behaviour rot in the dungeon of obscurity.

REPLY [2 votes]: Many excellent points are made in the above responses.  I suggest another point of view that may be important. It might be that at some point you will work in industry.  I've found that PowerPoint is often the preferred mode of presentation.  It is useful for everyone to learn how to use this medium if only because it may facilitate working with certain groups - industry.
For myself, I like the flexibility and simplicity of a blackboard.
Suggestion for whiteboard users - if you find a "dry" pen, throw it away!  All to often, I see someone discover that a pen doesn't write, put the cap back on, and return it to the tray.  Tossing it out would be helpful.
Final comments: 
Edward R Tufte 
Dr. Tufte, in my opinion, dislikes any PowerPoint presentation. The information desensity is just too restricted.  See his web site www.edwardtufte.com/tufte
Gapminder
There are some amazing examples of what can be done with a flexible electronic media in presentating data. See www.gapminder.org