With onset of Tango update for Windows phone OS, Lumia owners will be treated with enhanced multitasking. Windows Phone Tango will support 8 background apps switching instead of earlier 5 only.
Below is the screenshot of background tasks posted at XDA dvelopers forum. There are improvements in memory usage of applications as well, and it seems applications are using less RAM with Tango than the current 12070 firmware.
MMS has also got some improvements with delivery acknowledgement added with Tango.