Brief Description
The Property Bag Settings can store any metadata as Key-Value pairs such as connection strings, server names, file paths, and other miscellaneous settings needed by your SharePoint application.
Overview
Frequently, SharePoint applications retrieve configuration settings at run  time that were set when the application was installed or configured. To do this,  the applications must access the configuration information, which can be stored  in several locations. For example, configuration information can be stored in  the Web.config file, the SharePoint configuration database (for example, values  in the SPFarm property bag are stored in this database), or in a content  database (for example, in an SPList object are stored in the content database).  There are many challenges associated with these techniques. For example,  improper use of the SPFarm property bag can corrupt the SharePoint configuration  database. Also, although you can easily change the Web.config file with a  feature installer, it is much harder to make changes to the Web.config file  after a feature is deployed.
The SharePoint Property Bag Settings 2010  includes a hierarchical configuration manager that can safely store and retrieve  configuration settings at the following levels:
*Farm (SPFarm  class)
*Web application (SPWebApplication class)
*Site collection (SPSite  class)
*Site (SPWeb class)
*List (SPList class)
Downloads
Property Bag Settings  for SharePoint 2010
Property Bag Settings for SharePoint  2007