So I got tired of Gengo behaving like a queen bitch who doesn't let the cool people join the party and I'm putting this up. I am currently using WordPress 2.6 with Gengo 2.5.3.
Mind you, I am not counting the incompatibilities which have arisen in previous versions of WP and Gengo. On WP2.6 I have seen incompatibilities with:
Simptom: Blank pages across the board upon plugin activation.
Solution: Plugin removal from plugins directory on server.
Viper's Video Quicktags
Simptom: Administrator pages work but site frontend reports the following error immediately after activation:
Fatal error: Call to a member function on a non-object in /home/nllrnd/public_html/wp-includes/classes.php on line 39
Solution: Disable plugin.
I will keep adding to this list. I encourage you do to the same.