an intelligent upgrade
I just upgraded from 2.0 to 5.0 dreading the result as the industry normal now seems to be to mess around with a perfectly good interface, and slip in a few bell's and whistles, if possible messing up backward compatibility at the same time. Quark and Microsoft (Access, Excel, Word) are big offenders.
Not so Rhino. They decided to keep familiar menus, and to add separate menus for the changes. I haven't been using 5.0 for long enough to have discovered all the things that are new, but they range from slick little help-works (like gumball and smarttrack) to a real time alt-az facility which lets you show how the sun shines all day.
So, I was able to go right back to work in 5.0 on a drawing created in 2.0 using the same old familiar methods, free to figure out the what's new when it suited me.
To this end, the videos available are absolutely superb.