Saurik has released a revamped Theme Center for Cydia in coordination with MacCiti and implemented using the new Cydia 'whole package index'.
As I am not in charge of updating this area of Cydia (MacCiti/ModMyi are), users can actually expect to see new content on a biweekly (every two weeks, not twice a week) schedule. ;P
Right now, you will find a selection of themes from the top selling vendors in Cydia, as well as themes selected by the employees of MacCiti and ModMyi.
Currently, all nominations for additional Feature Themes, regardless of the repository they are hosted in, must be sent to either MacCiti or ModMyi.
However, Cydia 1.1, whose release is imminent, provides the additional platform hooks required to allow nominations directly from users to us.
We'll let you know when the new version is available.