[aviraldg]

Maybe because of the fact that bots usually scan the href attribute, but not the onclick attribute?

[flebron]

I would think any self respecting bot would notice "Hey, there's a valid email address on the page source code :D".

[dangoor]

If someone has coded up a "self respecting bot" then I think we've lost all hope against the spam harvesters (unless, of course, that bot's notion of self respect includes the recognition that spam is annoying to innocent people :)