For Mac:According to Gimp download page:
the 2.8.2 version GIMP runs on OSX natively. No X11 environment is required.However, I found it relatively tricky. If you download the dmg file from here (v2.8.2) which comes without any add-ons then you are in troubles. Since it doesn't have any add-ons in the package, then you have to manually install them by yourself, in this case, UFRaw plug-in.
On the other hand, if you are familiar with MacPorts and you can just type the command in terminal "sudo port install gimp" and MacPorts will install all related packages for you including UFRaw. Just so you know this version of Gimp must be run in X11.Well, I have tried to install Gimp via MacPorts but the UFRaw plug-in didn't work for me and to be honest I don't like the GUI with X11. So I would not recommend you to download and install both packages. However, if you download this package from here which is built by Simone Karin Lehmann, then your life will be much easier. It comes with many useful add-ons including UFRaw plug-in. I found it was much easier for me to start with Gimp.
For Windows:I have downloaded and installed Gimp from here on my Windows 7 and 8 machines and unfortunately the installation package doesn't come with UFRaw. Therefore I needed to install the UFRaw manually. Well, after a few tries, I found out it is very tricky to make UFRaw work. First of all, you can download Gimp from here and then download the UFRaw installer from here.
Please note, before you install the UFRaw, you need to install Gimp (either x86 or x64 version) first. After the Gimp is installed, please refer to the following screen shots to install UFRaw and the plug-in for Gimp:
1. Double click the installer and first installation screen should come up.
2. The installation package will default the path to "C:\Program Files\UFraw\" or "C:\Program Files (x86)\UFraw\" if you are using 64 bit Windows, but we don't want this default path. You need to find out where the Gimp was installed and install UFRaw in Gimp's installation path. In my case, "C:\Program Files\Gimp 2\". Please note, if you use "Browse" button to find Gimp's installation path, the UFRaw installation program will put "UFRaw" at the end of the path (C:\Program Files\Gimp 2\UFRaw\). Just remember to remove "UFRaw" because we want to install UFRaw in "C:\Program Files\Gimp 2\".
3. Click Next to continue.
4. The UFRaw stand alone application will associate the related file types.
5. Please note the "Destination location".
6. When the installation is completed, untick the "Launch UFRaw" and click finish.
7. Browse to your Gimp's installation path and it should look like below.
8. Go to the "bin" folder of Gimp's installation path and you should see "ufraw.exe" and "ufraw-batch.exe" in this folder.
9. Start your Gimp application and open a camera raw file. In my case, any *.CR2 file. You will see the UFRaw will start and you can adjust the image properties before using Gimp to edit your image.
In conclusion, I hope this article will help some people wanting to use UFRaw with Gimp.