While they are fun, I have a feeling that engagement or clickthru of the element they uncover may be higher without the layer of complexity on top of them.
Would this be against the new TOS for Twitter where you aren't supposed to modify the bird?
What I mean is that the link is plaintext, something like "Follow me at @username", which most people recognize as a call to action and a link to Twitter. Upon hover, the Twitter blue is applied with some animation, maybe something like the logo flying in. (yes, I know that screams against most people's personal design aesthetic here, but maybe it will work for some designers who want to stand out and are clever about it).
The main difference is that the Twitter logo is too discrete. There is literally no call to action and there's nothing about the Twitter logo that leads me to think that hovering over it will reveal the call to action. It's more likely to make me think: "This person works at Twitter!"
* edit: on reflection, I do realize that those Twitter icons, especially when used in conjunction with other social icons, are recognized as the "These are the social accounts", especially when they are in the footer. But I guess you'd have to do something different for the other social buttons?
If it's just one Twitter logo and no other social-button context, I still think that the call-to-action is too subtle.
