I can't remember exactly what was fixed in that time period but it would have been things posted in the forums, nothing extremely tragic comes to mind. I think the primary reason I shipped 18.104.22.168 was to include 10 new skins. The reason Mono users can't upgrade all the way to 22.214.171.124 is because of the use of Ajax UpdatePanel in the blog. This works with Mono svn trunk, I'm unsure if the ajax bits will be in 1.2.6 but don't think they are in 1.2.5.
I will say that the mono demo site is running 126.96.36.199, but it doesn't work under Mono 1.2.5, I can't login due to an error that I think is a mono bug in that version. Reportedly 188.8.131.52 works. I don't know if Eric has upgraded to 184.108.40.206 on GrokThis.net yet.
I think the upgrade from 1.x mojoportal will likely be challenging though doable, so much has changed. I would try a practice run on a local copy of your site and test it thoroughly. Whatever you do make sure you can get back to a known good state.
Anything I can do to help just let me know.
Hope you had a great Thanksgiving!
ps you may encounter some significant styling bugs if the upgrade succeeds. It can be fixed but might be a pain. The issue is the use of the CSSControl adapters which are not yet supported in Mono (though I have it on good word from Marek that its coming). So the skins are designed to style the ul and li elements as rendered on windows but on Mono the menu still renders as tables and the styling isn't setup for that.