Some Changes (Click the headline for complete change log):

• New: Refreshed user interface with new icons and visual styling. On Windows 7 and Vista, it is enhanced for Aero and "glass".
  
• New effect: Blurs -> Surface Blur, by Ed Harvey
• New effect: Distort -> Dents, by Ed Harvey
• New effect: Distort -> Crystalize, by Ed Harvey
• New: Russian translation.
• Performance and memory usage have been extensively optimized throughout the entire program.
• .NET Framework 3.5 SP1 is now required, which has many built-in performance improvements.
• Startup performance on most systems will be better by about 20%.
• Memory usage has been reduced when more than one image is open.
• The selection outline is no longer animated. Instead of "dancing ants", a context-sensitive "XOR" stipple pattern is drawn. This has allowed for improved performance and lowered CPU consumption (and longer battery life).
• On Windows XP, the Text tool has improved reliability and font selection (it uses GDI instead of GDI+).
• On Windows 7, the Text tool will use DirectWrite (instead of GDI) which gives better performance and greatly improved quality. On Windows Vista, you may install DirectX 11 to enable this feature; otherwise GDI will be used.
• All installation prerequisites are now installed automatically, such as .NET and Windows Installer.
• Updates are now downloaded in the background, and installed after you exit the application. In previous versions, this was a foreground task and you could not use Paint.NET while the update was downloaded.