40plus days are not very common, but they do happen. However, 35 plus days during the Australian summer (dec - March) are very common and quite difficult to deal with, especially if you have small children. They don't like being on the beach, it is too hot and the UV is very dangerous. Some nurserys and pre schools won't let the children out at all when UV levels reach certain limit.
From what I've seen, the only way to cope is to have a) very good air con and house designed to make most of shade, cooling etc. b)have your own swimming pool c) accept that for three months of the year you won't be going out much or you will be going from air conditioned car to air conditioned mall etc.
I guess after years in rainy gloomy England, whenever the sun shines I just want to fling open the windows and enjoy it which you can't do in Australia.
I never found mosquitos a problem. I don't know if that is a Perth thing. The flies are awful though. I always thought those hats with corks on were lazy cultural stereotype... ha! an essential, but then what do you do about all the flies on your back?
I was just thinking about what I've got up to with my daughter in England the last twelve months... we've been to Wales, Paris, theatres, museums, exhibitions... in Perth you can go to a)the beach b)scitech (children's science museum) or c) the zoo. Repeat ad nauseam until your ears bleed.
I'm exaggerating a bit for comic effect, but honestly, not that much.