I used KDE4 on my Netbook with KWallet storing/managing my WLAN-Keys. Then I switched to Xfce, which is nice, but when using Xfce, NetworkManager never remembers the keys and I have to enter them again (if I have them at hand!). When I go back to KDE, NM can access the keys (after I unlock the wallet). No matter if I enter a key in Xfce for the first time ever, or if I have entered them in KDE before (thus having it stored in the wallet), in Xfce, no saved keys are accessed, and no new keys are saved.
So I'm thinking this is because the keys are in the "wallet", which Xfce cannot/does not access. I have configured it to start KDE services, though ---> no change.