Gmail has added a bunch of new themes! The one they default you to is quite fugly actually, but some of the options are nice.
I haven't got access to the themes yet on mine, and honestly, I can't wait. I'm starting to get tired of the old look.
A toss up between Planets and Shiny... Might have Planets for the personal account, and Shiny for business ones - assuming themes are available on partner accounts that is.
I'm using Tea House at the moment, which isn't so hot in the morning, but I like the looks a lot at night. I also like cold shower. Really though, Classic style is still the most readable to me. Minimalist looks sort of ideal for Mac... loads of silver/grey. I'd like the bus stop theme if it didn't take up a bunch of horizontal space to stick in a silly giraffe between the rightmost column and the content.
There's one really cool feature I'd love to see... It no longer being in beta I suspect we'll see Duke Nukem Forever first.
On a more serious note, there are some pretty good features you can enable from the "labs" section. My favorite: "jump to label". Just type "gl" then start to type a label, and you can quickly open the convos with that label.
Not sure... I saw the hotmail themes about a week before I saw the gmail themes. The new hotmail layout actually seems to be sorta decent. If they would drop the giant banner at the top of the page, it would actually be very nice. I pretty much only use my hotmail for spam collection though (I register for web sites with it).
Grrr. They switched me to the default before adding the themes tab to my account. I turned off labs and it was still there, but there was a link to the themes tab (despite there not being a themes tab) and I changed it back to classic.