The Personal version has limits on certain functions and the Premium version has none. However, when it comes to deciding which you should purchase for your application, consider the License Agreement as well.

	Personal	Premium
Read/Write All RSS Versions
Read Password Protected Feeds
Read feeds Windows Common Feed List
RSS Auto-Discovery
Advanced RSS Discovery
RDF Support
Read/Write RSS Clouds
Read/Write RSS Enclosures
Create Extensions
BlogChannel Extension Support
Creative Commons Ext. Support
PhotoAlbum Extension Support
Exception Logging Support
Pingback Support
Trackback Support
XML-RPC library Included
DB Helper Library Included
UniversalDateTime Class
Captcha Controlled User-Input
API/Namespace Documentation
VB and C# Snippet Support