The Drupal association keeps a list of hosting companies the support hosting Drupal. There are 216 contacts in our mailing list. We would like to send a detailed email explaining what Drupal 7 means for hosting companies. We can go over the basics of systems requirements, but we need to educate hosting providers about differences and benefits of Drupal 7. We've already seen some concern raised over the number of tables raised. We know there's concern about the performance of Drupal seven, but we know that services like Varnish can greatly improve anonymous page caching.
http://drupal.org/requirements
Choice bits:
Drupal 7 will only support MySQL 5.0.15 or higher, and requires the PDO database extension for PHP (see PHP section below).
Drupal 7 will only support PostgreSQL 8.3 or higher
Recommended: PHP 5.3 for Drupal 7
Required: PHP 5.2.5 or higher for Drupal 7
PHP 5.2.5 or higher is a requirement for Drupal 7. (Distributions of PHP 5.2.4 that include backported security patches, such as the version included in Ubuntu Hardy, should also work with Drupal 7.)
Drupal 7 core requires 32MB. Warning messages will be shown if the PHP configuration does not meet these requirements. However, while these values may be sufficient for a default Drupal installation, a production site with a number of commonly used modules enabled (CCK, Views etc.) could require 64 MB or more. Some installations may require much more, especially with media-rich implementations. If you are using a hosting service it is important to verify that your host can provide sufficient memory for the set of modules you are deploying or may deploy in the future.
Drupal 7 may require the time parameter to be at least 30 seconds.