Having done this a few times I now only export and import to and from the same and latest build. That means making a copy of your old site, upgrading it, then exporting.

• Roles are exported but users are not - So if you have users you can't lose then you will need to find a module that will do the users for you.
• Some modules will not export content even if they have an export function on the menu - e.g. Blog
• Some modules export content but with buggy behaviour - e.g. Announcements
• Ensure that your skin is in the portal folder as in; uploaded via the admin account, not the host account.
• Ensure all modules used are already present in the destination portal or they will lose their places.
• Even if they are present, be aware that most thiurd party modules don't export content and often don't seem to even export their settings, as in, the module turns up but is not configured and has no content.
• Some modules have problematic behaviours that need to be fixed when the location of the install changes - e.g. the Blog has folder paths that have to be manually configured.
• Avoid using Friendly names for modules
• Avoid using Friendly names for portals
• Ensure that you set and reset proper file permissions and also do manual file-syncs in the DNN File Manager whenever you add or remove files via any method other than the file manager.
• and as said above - Avoid bugs by not exporting from an older version of DNN

Basically, you can't export and import a complete DNN portal yet. But you can export a portal as a partial framework with many components in place. You can then count on having to add users, add content and reconfiguring things to make it work again.

Hope that helps.
Rob