Wubi development testing is typically under-represented by the Ubuntu community because it's mostly used by newcomers to Ubuntu (and many hardcore users don't have Windows). Wubi is the first impression of Ubuntu for many, and so it's important that this is a good experience. Since 11.04 was released, Wubi has been very stable, but there's always room for improvement and to get rid of any irritating bugs.
With that in mind there has been a call to testing on ubuntuforums.org. If you have the ability then please help out, and provide feedback in that thread and/or file bugs on https://bugs.launchpad.net/wubi/+filebug.
There are a number of ways to run Wubi tests:
1. Download wubi.exe and run it standalone (during dev you can get it from here)
2. Download the Desktop CD ISO, burn it to CD if it fits (or DVD), and run it from there.
Note: each time you install Wubi it uninstalls any existing Wubi install (so if you use Wubi normally you can't easily test it unless you are comfortable backing up your current install).
There are a few tricks you can use. E.g. running wubi.exe standalone will download the preinstalled images i386.tar.xz or amd64.tar.xz from here. That's a 500MB download each time you run it, so instead you can download it once, save it, and then point it at your local copy with a command line option. This saves a lot of time if you are repeatedly testing. e.g. for a 32 bit pc:
You can also test the ISO install without burning a CD or DVD each time, by saving it in the same directory as wubi.exe (which you can get off the ISO or use the standalone download).
If you run wubi.exe standalone, but install something other than 'plain' Ubuntu it will always download the ISO instead of the disk image. You can also override this download by copying the ISO into the same directory as Wubi.exe, but note that since the ISO changes frequently in development, chances are it will try to download a new one anyway. To get around this (if you know the MD5SUM of your ISO is good,) you can disconnect from the Internet for the first part of the install.
Remember you can use Wubi to install:
Pay attention to the latest wubi.exe revision .e.g as of the time of writing, the latest is wubi-r256.exe. This version won't install Edubuntu, but forthcoming ones will. And whenever a new revision is published it's important to retest to make sure the bug fixes work and make sure there are no regressions.