We also just switched to Rev. 20 and it is, so far, virtually painless. Specifically in my group, we decided a on a certain day to all start using the new revision and did. The only trouble you should have is if you ever try to bring something up in Rev.19 again...won't work. My suggestion is move to 20 and don't look back. All your models, assemblies, drawings, etc. will update themselves as they need it.

Later....

Version 20 may look somewhat challanging due to the different format, just use it. It will only take about an hour of playing with it and you will like it. Version 2000i is even better, it has the same look with extra goodies, the release notes are a good place to see the improvements. You don't need to worry about updating your parts, assemblies, and drawings. Just bring what you need into session as ussual and ProE will handle the rest; this also assumes you will have only the current version of ProE running; the part, assembly, and drawing, files are not backwards compatable.

I have been using 2000i for several months. It is much better than 19 or 20. They have added lots of extremely useful shortcuts to the model tree and other locations.

I strongly recommend using this version.

Also, in regard to upgrading from older versions: the statements made above are absolutely true. The only issue that should arise is backward compatibility. And this issue will only arise if your organization is running more than one version at one time. Also, the native Pro/E files are not compatible, but I'm sure you could export an IGES/STL file from 2000i and import it into 19/20. You indeed lose some of the functionality but you get the basic part.

As those before me have stated, upgrade ASAP. I would be shocked if you regret it.