The SSRS 2008 R2 release in SharePoint mode allows two forms of reporting:

• Out-of-the-box (OOTB) Local mode reporting: In this case, SSRS 2008 R2 introduces the ability to render reports without an integrated Report server. Details on local mode reporting with SharePoint integration can be found @ http://msdn.microsoft.com/en-us/library/ff487969(v=SQL.105).aspx. From an install prespective you only need to install SSRS 2008 R2 RTM Add-in for SharePoint 2010 on SharePoint 2010 RTM Web-front-end(s) to have the ability to render uploaded / canned reports (.rdl files) for:
  
  1. SharePoint Lists reports: available in SharePoint 2010 Foundation Editions or higher. 
  2. Access reports: available in SharePoint 2010 Editions that Access Services is supported in. 
  Point to note: You need to turn on ASP.Net Session state as well, by opening the SharePoint Management Shell and entering the command - Enable-SPSessionStateService. Next, the command will ask for a DatabaseName value that you can provide say "MySessionDB". Finally, perform an IIS reset. 
• Connected mode Reporting: This form of reporting is allowed when you have an SSRS Report Server integrated into the SharePoint farm as well to enable full end-to-end reporting that existed in prior versions and is now available in SharePoint 2010 with the SSRS R2 RTM Add-in for SharePoint 2010. Details on configuring connected mode @ http://msdn.microsoft.com/en-us/library/bb326213(v=SQL.105).aspx. There are 2 report server major versions that can be used in this form of reporting for SharePoint 2010: 
  1. SSRS 2008 R2 RTM report server: In this case, with SSRS 2008 R2 RTM Add-in for SharePoint 2010 and SharePoint 2010 refer to the what's new in SSRS R2 functionality for information on what all is supported @ http://msdn.microsoft.com/en-us/library/ee210710(v=SQL.105).aspx 
  2. SSRS 2008 Report Server: A patch is needed for SSRS 2008 Report Server SP1 CU8 (planned for released in May, 2010 @ http://support.microsoft.com/kb/981702/en-us) to enable its support with SharePoint 2010 and SSRS R2 RTM Add-in for SharePoint 2010. Additionally, in this configuration existing SSRS 2008 in SharePoint mode functionality that SharePoint 2010 supports via backward compatiblity with SharePoint 2007 is available / supported . New SSRS 2008 R2 in SharePoint mode functionality like Alternate Access mapping, Access Reporting, SharePoint List reporting, etc. OR new SharePoint 2010 functionality like Claims etc. is not supported in this configuration.

thanx,
Prash