WPA2 without MAC filtering?

WPA2 is considered safe. MAC filtering won't really help because it's possible to spoof a MAC id.

so even without MAC filtering it isn't possible to connect to WPA2 networks without the key?

Theoretically, while older systems like WEP are regarded as simple to penetrate WPA2 is safe.

In all this the main concern is who, not what. Penetrating WEP isn't something you or I would choose to spend our time doing -- so you can assume that in the small area of your average neighbourhood viably covered by your wifi signal you mainly need a security system that stops anyone blundering onto your system by accident or through casual curiosity.

Interestingly, while trying to set up a spare router I logged into a neighbour's system which had WPA2. I was momentarily puzzled to be welcomed by the setup screens of a different brand of router to the one I thought I was addressing.

I won't elaborate in order to avoid tipping off hackers but I was able to recreate the scenario later with some trying. So I know the how but remain puzzled at why. The issue seems to relate to a router from a known brand, but probably only one model and possibly only a variant supplied by an ISP in the UK.