Since I have been a Sprint user for coming up on a decade now, I took its service level for granted. I am going to attempt to rectify that now with some basic notes on how the service is with Sprint and the Pre.
While I cannot compare against personal experience (see above), I do have friends with a mix of cellular carriers and I can compare against them. In my area (Seattle), I have rarely noticed an instance where I got worse service than others around me and have noted several times to be getting any/better/more reception in places that my friends are not.
And for me, that has always been my biggest boost about Sprint. I seem to get service everywhere (aside from a trip through South Dakota) and other than when I had to order a new phone and change service plans, I have never even had to interact with Sprint's customer service, which is what most complaints about Sprint seem to stem from. Also on the plus side is that I have the least expensive bill of anyone that I know and that even includes some friends who do not have any sort of data plan on their phone.
Not only is the service prevalent but it is fast as well which is good because I often have to use Sprint's service to cover for the completely abysmal performance by cable and internet company (No, it's not Comcast. I wish I had Comcast) which constantly drops my internet service for hours at time. That has resulted in me spending time actually forced to use my Pre's web browser to get work done and that it can cover for that in a pinch is another feather in Sprint and Palm's caps.