I have two Streetpilots, an i5 and a C330.
I bought the CD for the 2008 update from a local map store.
The maps are so much larger in file size now that neither of my units would take all of North America.
I had to make a choice to install either the US and southern Canada, or Canada and the northern US.
I put one in each unit after complaining to Garmin direct and they sent me a free CD so I could do it. (The CD is coded to one unit only and won't allow you to install to two different units.)
One thing to know here though. I had to use Windows XP to install the updates in both units. There was a glitch that did not allow a Mac to make the upload and I made Garmin aware of it, thus the free CD.
The CD cost $79 plus tax BTW.