Recently we upgraded a Plone 3.3 site to 4.3. Here are some thoughts regarding this.
Recently we moved a site from a long-time customer to Plone 4.3.
First off, the list of step to follow in http://plone.org/documentation/manual/upgrade-guide/version/ were quite exhaustive. There were some things that we did differently:
We went straight from Plone 3.3 to 4.3.3, skipping the intermediate versions (4.0, 4.1 and 4.2). For our site this worked.
After that, we ran all upgrade steps at once.
We had to manually remove some Javascripts (mostly Kupu) from the registry, in order for TinyMCE to work.
The sooner you upgrade to a more recent stable version, the smaller the hassle. Also, there’s a performance improvement (see image), and some nice new features. See http://www.sixfeetup.com/blog/five-reasons-why-waiting-isnt-the-best-upgrade-strategy for more reasons to upgrade.