To everyone wanting text buttons, consider that a surprisingly large amount of the population has literacy problems (perhaps an email client isn't the best example for this, since you're using it to read and write words, but consider the general case). Icons are going to make their life easier (assuming there isn't room for icons+text all the time). This is an counter-point/trade-off to vision-impaired accessibility where you need words everywhere.
Icons are hard (to get right) in general. Do you stick with skeuomorphisms when half your user base know them well, but the other half have no idea what they mean (e.g. floppy disk to save)?
Maybe some people are more wordy, and some more visual? You'd be surprised at how people adapt to not being able to read - there is literature of children who 'fake' reading - they essentially memorise the shape of a thousand or so words (over the course of their school) so it appears they can read to some degree, but have no idea when they come across a word they haven't memorised.
Icons are hard (to get right) in general. Do you stick with skeuomorphisms when half your user base know them well, but the other half have no idea what they mean (e.g. floppy disk to save)?