I upgraded to WordPress 2.1 this morning and the whole process was remarkably painless.
The entire process took about ten minutes - the majority of that time was spent on backing up the previous version and FTP’ing the new files into place.
Of course, if you are a client of mine and I maintain your blogs, it actually took waaaaaaaaaaaay longer. Hours of research, planning, etc. were involved and if you need me to upgrade your blog, my invoices would