I would also encourage people to vote for this idea: New UI Collateral for Admins.
https://sites.secure.force.com/ideaexchange/apex/ideaview?id=08730000000712vAAA

Hi I am a developer and would like to test my vf pages on new interface themes. However the wiki page is instructing, to sign in using partner program to enable the new UI.
Please instruct how should I proceed.

Jason – The Spring ’10 Preview documentation for Visualforce can be found here:
http://wiki.developerforce.com/index.php/Documentation#Apex_and_Visualforce
This documentation is more targeted Developers than it is at Admins, but you may find it useful.

The fact that the new interface theme is optional will make life difficult for ISV partners.
Which UI should we optimize for? We use Salesforce’s native styles & visualforce components, but there are still times when I have to trade off between “looks good in the old interface” and “looks good in the new interface”.
How will I know when the majority of my customers have switched? We have far too many customers to reach out and ask individually. Will salesforce collect this data & report it back to me?

John – Note that if you’re using standard Salesforce UI components in your application, you shouldn’t have to do anything to optimize your application for the new theme. The only scenario in which you might need to account for it is if your application includes custom CSS that mimics that of the Salesforce UI (i.e. matching colors). In that case, it’s not a question of optimizing for one theme or another — you can simply craft your application to include the correct CSS for either the old or the new theme. See:
http://www.salesforce.com/us/developer/docs/pagespre/index_Left.htm#StartTopic=Content%2Fpages_styling_salesforce.htm|SkinName=webhelp

We were told on the Salesforce development course, that individual customization is now easier with theme 3.
We are waiting for a way to extend the standard css with our own css.
Otherwise we have to recode every standard side by means of a new visualforce side (specifying our custom css).
This is even more tedious, because any in such way created visualforce side will adopt the look and feel of our css, but when you switch to “modify” the look and feel will change back to standard salesforce, and needs massive manual coding in order to adop to our own css.
We are developing custom force.com applications for clients, and urgently need a way to give appliations a client specific look and feel, without the pain of recoding already existing salesforce code with great effort.
Thanks for any hints

OK…my instances have been upgraded to Spring ’10…and there’s no option to enable the new UI using the instructions provided. Did the UI rollout get postponed? Or has the method to enable it been changed?

Hey Michael — The new UI theme is not slated for release until Feb 12th.
…stephan

Still on track for a release today?

OK it’s the 12th, where is the new UI!???!?!

I just called them and they said due to problems they are predicting a March release of the new UI.

Anyone know when the new UI is going to be released?

It’s been released!
I’ve got on my DE org.

I thought the related lists were going to be moved to the left side? Is this an option?

I think you are not quite right and you should still studying the matter.