Pitfalls of upgrading to iOS4.2

The decision to upgrade to iOS4.2 should not be taken without considering the following:

• once you upgrade you cannot easily downgrade to the previous OS (along with gnashing of teeth and muttering indelicate words, you will  probably need a previous version of iTunes (which is usually upgraded with each OS release), and the backup copy of your iPad OS (which, oddly, iTunes deletes once you upgrade))
• do the apps that you cannot absolutely live without, work with the new OS? (apps that have not been written properly just stop working and if it's an app you rely on daily, you either have to do without, find an alternative app or downgrade back to the previous OS-- see previous bullet point)
• do the new features of the OS outweigh the possible loss of some of your favourite apps?