My wi-fi had always been great with regards to use with my Windows 7 Desktop computer, my iPhone 3G and my iPod Touch, but (as some other users have experienced) I found it really bad with my new iPad 3, especially when downloading from within apps, such as downloading books using the Kindle app.
Last night while fooling around, I came up with a solution that really speeds up my wi-fi. The only caveat (and it is a BIG one for some people) is that it requires removing security from your wi-fi network.
This is my setup:
* Thomson SpeedTouch 536 (the one that Telecom supplies). I have the wired version, but plugged into my -
* Apple Airport Express
So after trying in vain to download a Kindle book that is only a couple of MB in size (really it was so bad it bottomed out at 25% downloaded, and after multiple tries, failed at even a few percent), I did this by trial and error -
1. Download the FREE Airport Utility from the App Store onto my iPad. I think I already had it on my laptop from when I set up Airport Express, but I couldn't be bothered booting up the laptop again.
2. Follow these steps using the Airport Utility - Tap on Network -

2. Tap on 'Security' -

3. Tap on 'None' -

Then go 'Done' etc. If you try to exit it will tell you there is a security issue, but just tap 'Ignore Issue'.
Following these steps has now made the wi-fi on my iPad 3 a pleasure to use. As I say, this is not for everyone, because it removes the password from your wifi. It's OK for me because I am out in the country and my wi-fi doesn't reach that far (even struggles to reach the other end of the house), so USE AT YOUR OWN RISK.