It's not so much I don't like the idea of Personas. A skin I can change with literally one click, not causing me to restart my browser? Awesome! The real trouble is the implementation. If you have the tab bar, navigation bar, and bookmark toolbar, there is only ~100 pixels to show your Persona's image. (For me, it's 110.) Without the bookmark toolbar, it's 32px less, and even if you have addons that let you have multi-row tabs or bookmarks, it still doesn't add up to much.
For some Personas, this is fine. My favorite right now is called "Aurora Australis" and because it's basically just a gradient (albeit a very beautiful one), it looks good no matter how much of it is showing. But when it comes to other Personas that focus more on an image, like maybe this one or this one, you don't even get what the preview is; you just get the very top of the image. And then in addition to that, you've got things like the address bar, search bar, tabs and bookmarks all covering it up.
My opinion is really that Personas are good for gradient-type backgrounds and not for specific images. Either that or the Persona maker needs to hike the image up as high as he can so we can actually see it, or better yet, go simple. Otherwise, I'd say that a Persona is completely useless, because I want to see Link, not Link's hat, covered up by icons.
You may have a different opinion than me, and that's fine. I really haven't thought heavily about it or browsed through a ton of the Personas, so I'm always willing to change my mind about it. But it really makes me feel as though I'm right when I see Yahoo!'s own Persona, you'll notice that it (a) is very simple, and (b) has a small image, placed very high up. Also, scrolling through the "Popular" section, I see that a ton of them are abstract, meaning that you can basically cut it off wherever you want and it will still look good.
I'm the farthest thing from a graphic designer, but as someone who does look at graphics, I would propose 3 choices to anyone wanting to make a Persona:
- Do a gradient (something that has no beginning or end)
- Do something abstract/fractal/what have you
- If you choose an image, keep it small and simple