Just a quick posts to talk about a number of issues I have seen with slow wordpress performance after a 2.7 upgrade.
What I Have Seen?
When you access the front end of the blog, things run especially slowly. On a number of blogs I have seen the theme load but no posts.
When you attept to connect to the backend i.e. wp-admin the problem is not re-created.
Theme Schmemes
The problems I am seeing are with themes which have not benn upgraded to make use of the new 2.7 functionality.
I assume that they are trying ot run a previous version function, and when this does not work, the system retries for a period before failing.
Testing For A Dodgy Theme
There is a very quick test to see if your theme is causing your issues. Simply change your theme to the wordpress default theme, and test your blog again. If performance improves the theme is the culprit.
If you are running a cache program disable is to ensure nothing is cached and the latest file are being served up.
What to Do?
Go back to the web designer who developed your theme and check to see if this is a know issue. It is quite probable that a 2.7 version of the theme has been released.
Download this latest version and upload it to your blog, fingers crossed the problem will be solved.