Earlier this year (March, 2008) Microsoft declared (in an Exchange Team blog) that Public Folders will be retained in the next version of Exchange (code named E14). This means that Public Folders will be supported for 10 years after E14 is released:

http://msexchangeteam.com/archive/2008/03/31/448537.aspx

An earlier blog by Terry Myerson in 2006 entitled, "Exchange 12 and Public Folders" stated Public Folders were being "de-emphasized". While Exchange 2007 (which retained Public Folders) is supported for 10 years from release, those new to public folders were encouraged to look at SharePoint. This use of the word "de-emphasized" was interpreted this to mean that "Public Folders are dead, and you need to migrate to SharePoint now!" . At the time what it really meant was that Microsoft would support public folders for Exchange 2007 (E12), but would not guarantee that they would be supported in releases after E12, nor would additional feature content be added to Public Folders.

As we know now, that position has changed somewhat. Microsoft will now continue to support Public Folders in the next major release of Exchange Server, after Exchange 2007. This means Public Folders will have full support for 10 years after the release of the next major release of Exchange Server.

Despite the surprise from the marketplace, Microsoft pointed to the fact that they had stated this 'way back in 2006! They pointed to a blog post by Scott Schnoll from June of 2006:

We get a lot of questions on Microsoft's strategy for public folders in Exchange Server. For those of you who are still wondering what the fate of public folders are, be aware that:

• Public folders are present and FULLY SUPPORTED in Exchange 2007.
• The next major version of Exchange Server AFTER Exchange 2007, will also likely include public folders.
  

Microsoft's stated direction for public folders is the SharePoint product suite. The company has strongly suggested to customers that it should be moving to – or at the least launching any new collaborative data on -- Office SharePoint Server 2007. SharePoint, while it does a GREAT job at some things (document libraries come to mind), it does poorly at other things (threaded conversations) and does not do some things at all (replication of content to many sites).

Also lots of IT shops are postponing a transition because it costs money, and they say the public folders work just fine for today's purposes.

ExchangeWise Strategy

ExchangeWise (Pty) Ltd is a specialist software house focusing on the development and marketing of applications and utilities that provide functionality in the core business areas of messaging, collaboration, customer relationship management (CRM) and knowledge management. The company focuses primarily on Microsoft’s technologies and product and for this reason most of the company’s offerings are designed to enhance the functionality of Microsoft Exchange Server and its primary client, Microsoft Outlook.

The company has been careful to develop a range of products that maximize all the features and advantages of Public Folders while at the same time giving users plenty of alternatives to migrate away from Public Folders should a customer feel this to be the appropriate course of action. Some of these products are:

1. MX-Contact Outlook-Folder Editions: MX-Contact (www.mxcontact.com) is an Outlook-based CRM that has 6 different versions available catering for a single user through to an enterprise with thousands of users, with data storage in an Outlook Data File, Exchange Server Public Folders, or Microsoft SQL Server. The WorkGroup and Corporate Editions utilize Public Folders directly for data storage.
2. MX-Contact SQL Editions: The MX-Contact SOHO and Enterprise Edition still use Outlook forms but store all data in SQL Server, so that users enjoy the benefits of having all the extended functionality that MX-Contact provides still within their Outlook profile, while at the same time IT Managers are comfortable that the data is stored in a true relational database that is robust and scalable, i.e. SQL Server.
3. MX-Folders: MX-Folders is an Outlook Add-In product that allows users to utilize existing Public Folders, along with their custom Outlook forms, but store the data directly in SQL Server, rather than in the Public Folders. This enables one to continue reaping the investment made in customizing the forms but at the same time have the data stored in a true relational, scalable database, namely SQL Server, with its corresponding advantages, namely easier reporting, data integration and backup.
4. MX-Contact.NET (www.mxcontact.net): MX-Contact.NET is a Microsoft.NET-based product that uses the same database as the SQL Editions. While it is integrated with Outlook, it does not use Outlook forms or Public Folders at all. Moreover it is a web-based product that that either be hosted internally or hosted on an ISP’s server. So even if Microsoft had eliminated support for Public Folders, the company would already have been in a position to immediately migrate the existing customers of the MX-Contact Workgroup and Corporate Editions (which store their data in Public Folders).
5. MX-Sync: (www.mxsync.com). MX-Sync is an Exchange Server to SQL Server synchronization utility that is designed to synchronize items bi-directionally between a user’s personal folders in Exchange Server (Inbox, Sent Items, Contacts, Calendar, Tasks, etc.) and a set of SQL Server tables, or a set of Public Folders (either standard or MX-Contact) and an equivalent set of SQL Server tables (either from a non MX-Contact CRM system or from an MX-Contact SOHO or Enterprise Edition system). Thus MX-Sync can be used to keep Public Folder data and SQL data in sync, so as to maximize the advantages of each platform.

Summary

Public Folders continue to be one of the most popular features in Exchange Server although Microsoft has been trying to get IT shops to change users' habits and move content to its SharePoint platform.

Fortunately, now there is no big rush to move off of public folders today because we can expect full support for Public Folders at least through the life of Exchange Server 2007, which goes to 2016, and beyond to probably 2020, the end of the extended support lifecycle of E14.

References
Public Folders and E14 - The Next Version of Exchange
http://theessentialexchange.com/blogs/michael/archive/2008/03/25/public-folders-and-e14-the-next-version-of-exchange.aspx
Users hold fast to public folders despite iffy future
http://searchwinit.techtarget.com/news/article/0,289142,sid1_gci1267231,00.html