I'm thinking off trying some but if it takes any sensation from other half does this defeat the objective. Or does it not effect the lady parts, not sure weather I'm a bit thick or just nieve.
The idea is that you apply it and let it be absorbed, so that the cream or spray itself never actually comes in contact with your ladyfriends.
Oh I tried this for anal! I hated it paulsballs. I couldn't feel my vibe up there at all. Tried it one more time with the OH and nothing. I would never go there again if you paid me.
I need to feel...x
I use it and it works well for us (I actually favour the Durex Mutual Climax condoms).
Now obviously using a delay cream with a condom kind of bypasses your question as there is no way the delay cream can contact your ladies parts :)
I have also used just the creams on their own though, and as others have said so long as you apply it early (perhaps as part of foreplay) then allow it to soak it your ladies parts shouldn't be affected by it at all. Be aware though, most of them take about 5 minutes to take effect (at least the ones I've tried). Do NOT make the mistake I did the first time I tried them... coated the head of my penis with the cream, didn't seem to have any effect so applied some more... needless to say 10 minutes later I was completely numb - no feeling in the ol' chap at all 
Apply just a tiny amount on your most sensitive areas, (I find a small dab on the frenulum on the underside, and sometimes a small amount around the ridge of the head works well), and give it 5 minutes. It is a bit of trial and error, but that can be half the fun, working out how much works for you.
Good luck, and enjoy!