I did it for a year, and for us it was the biggest waste of money ever!
I guess it could be good if the location is handy (our was an hours drive away) If you are keen on buying lots of big branded expensive items and if you are prepared to stick it out long term.
We joined up thinking it would be great for baby products too but when we finally had a good look we noticed they only seemed to stock a few of the really expensive brands, I guess its good if thats what you want to go for us personally we were just as happy for the middle of the road stuff which we could still get cheaper.
Nappies (huggies) we found we often cheaper at pak'n'save, and a few other things we found we could get just as cheap or cheaper from the warehouse. Board games, lego, kids toys etc.
With place like the Warehouse having access to major brands through parallel importing the prices are virtually the same because of sheer volume.
In my opinion I wouldnt do it!