Why wouldn't you recommend this? I've seen several posts here that advise people to do exactly this, yours is the first I've seen that makes it sound like a bad idea. I was planning on restoring my new 3GS from a backup made with my 2G, so if you have any credible sources that point to this being a bad idea I would love to see them!
scroll down to troubleshooting and go to the section on
backups. It appears that restoring from a backup is apple's
preferred method of moving to a new iPhone.