Warranty upgrade info?

[alpuzz]

When I bought my T43 2668-75U, it came with the standard 3 year depot warranty; However, my rep told me that I could upgrade to on-site at any time during the life of my current warranty.
If this is the case, then I have a few questions:
1. for those who have had on-site service, how was the experience? The last time I dealt with something like that was about 10 years ago when I had a Toshiba Tecra. The service call was handled by Banctec. First, I had to go through a diagnostic with a Toshiba support person. Once we determined which part was at fault, they had that part shipped to me. after I received the part, I called back the service center, and they scheduled the visit.
It all ended well but my point is that from beginning to end, the whole process took about 3 days. I'm guessing that depot service would probably result in slightly longer average downtimes, but how much of a difference would the on-site actually make? Does IBM use the same basic process as I described above or have they refined things at all?

2. If I can upgrade the warranty at any point, then could I just wait to see if the machine ever does need to be serviced, and upgrade to on-site just before placing my service call?

Thanks,

--Al