After upgrading my first site, and removing the two offending extensions which started to cause 500 Internal server errors. Finding a replacement/workaround for FoxContact was easy and built into Joomla anyway, JCK Editor Manager also had problems. I've temporarily removed JCKEditor and permanently removed FoxContact.
All other Extensions that I use accross my other sites seem to be working flawlessly. That is K2, Kunena, JCE, PodcastManager, Joomla Admin Mobile, Community Builder and Jevents. I've probably missed one or two.
Overall, I am pleased with how the upgrade process went and am very happy with Joomla! 2.5. Even with the issues I had with a couple of extensions, which will most likely get updates in the near future and hopefully solve any issues for others.
If you are dead set in needing extensions and they are not stated to support Joomla 2.5, I suggest staying with 1.7 until updates for those extensions are available for Joomla 2.5.
Otherwise, I recommend upgrading to Joomla 2.5.
