Thanks in part to a computer hardware retailer being closed, KDE 4.11 (and KDE 4.12) will offer improved system memory usage.
A KDE developer, Sergio Martins, was going to buy additional memory for his PC but with the computer shop having been closed, instead he decided to take care of some open KDE bugs concerning memory usage. Sergio was able to fix a number of KDE application bugs for the upcoming 4.11 release.
Among the memory hungry issues he resolved were with maildir, the Akondadi service process, Kontact, KOrganizer, KAlarm, and MySQL. Besides the work of Sergio, other KDE developers have been focusing on performance/memory improvements too, particularly around KDE's Nepomuk and Akonadi components.
Details on the resolved KDE memory usage bugs can be found in this KDE.org blog post
The KDE 4.11 Release Candidate
just came out this week while the official release of KDE 4.11 is expected in August.