I just installed the
XCarLink iPod integration kit in our 2007 Mazda5 a few weeks ago.
I found it relatively easy because the Mazda5 center console is not too difficult to pull apart and put back together. The installation took me a couple of hours -- probably could have finished it sooner but I was looking at different options for where to place the control unit and run the cords.
Ultimately, I wound up installing the control unit inside the glove box (used two-sided sticky tape and adhered the unit to the back of the glove box on the top shelf; all of the cords were tied together or attached to other cabling using zip ties) because the iPod cord is not very long and I wanted to keep options open for using docks on either the center console or dash. For now, the iPod stays inside the glove box, and it works fine because the XCarLink unit allows you to skip tracks, change playlists, and fast forward/reverse using the headunit audio controls. Sound quality is a little on the harsh side, but still a big improvement over the FM modulator dock I previously used.
As far as the installation goes, I rounded up several installation guides before getting started. The Mastersheet from Crutchfield and the installation instructions for Mazda's iPod integration kit were most useful (mazdaparts.org posts PDFs of the instructions). The Mazda instructions install the control unit in the upper center dash (behind the LCD display) and then run the cords into the glove box. I opted to install everything in the glove box (I didn't bother to remove the glove box door -- for one thing, the instructions were very confusing). In addition to the iPod input, the control unit also has an additional aux input. So, having the unit in the glove box also gives me access to that input if I ever want to connect a non-iPod player to the car.
http://www.ehow.co.uk/how_7387356_remove-stereo-mazda5.html
http://www.mazdaparts.org/mazda5-ipod.html
The only real hidden trick that I needed to navigate was putting the shifter into neutral before the center console would come out (assuming you have an AT). Since you're disconnecting the battery before starting the installation, you would need to put the car into neutral first. Otherwise, everything was fairly straightforward. By comparison, my 2012 Mazda3 looks like much more of a pain to disassemble (since that car already has an aux input, I just run it from an iPod charging dock).