Originally Posted by Mr. H
The problem is twofold:
1.) They violate Apple's own Human Interface Guidelines (I hate it when Apple does that) (take a read of page 3 from Ars' Tiger review: found here
2.) In Mail, at least, they are one size only, rather than having a choice between "large" and "small". This will be less of an issue if they every get resolution independence working properly.
I do like that they bundle together similar/related actions. Ars' claim of violating the guidelines is a bit debatable, in my opinion. In the given example, the user does have the option of getting the actions independently or together, and I don't have any trouble identifying at a glance the action a button takes. Large & small is a legit complaint though.
I will say that I don't use Mail or Xcode (I don't code much). For me, Mail is not flexible or efficient enough. Thunderbird is flexible and reasonably efficient. Heck, Mail's rate of importing mail from Thunderbird doesn't exceed ten a second, maybe it's five, taking an hour to import mail from another program. I like that Thunderbird offers buttons on every mail line item
to mark that given line item as trash or mark as read, it requires a lot less key pressing or mousing around than Mail for those same actions.