When I had the iPhone / iPod touch UI Support 1.0 plug-in enabled, I was unable to select the 8 of the 9 Settings pages under the Preferences menu. Clicking on any of the other settings would take me right back to the General Settings page. Once I disabled the plug-in, things went back to normal.
Has anyone else experienced this incompatibility?

I have the exact same issue.
Ah, so that is causing it! Same here!
Hi guys, I've had exactly the same behaviour. Reported it as a bug before reading this (typical eh?)
I'm seeing other posts on the same issue, I guess this is fairly common
Ah-ha. Mystery solved. I hope this one is resolved either within MT or the iMT plugin swiftly, because iMT is pretty crucial to some of our highest traffic bloggers.
There have been fixes made to iMT - that lives in our subversion repository. You should be able to execute the following:
svn export http://code.sixapart.com/svn/mtplugins/trunk/iMT
If not we can work on getting a new build of iMT out as soon as possible. I will email Brad (the author) to see what can be done.
Thanks Byrne,
We're unlikely to go to 4.2 on our main system until mid-July, so that gives Brad a wee bit of time. :)
Good news! I just uploaded the latest version of iMT - the iPhone UI for Movable Type. The latest version is 1.02 and can downloaded from the iMT homepage in the plugin directory.
Is the native iPhone app that was announced Monday going to work with MT, or is it going to just be for TypePad subscribers?
The native iPhone app announced and released Monday works exclusively with TypePad. As to whether MT will get such an application that is another question. I certainly hope so.
Just be patient, and let's see what turns up. :)
And now I had this issue. It's so nice to have this documented... and to be able to lean over to Brad and ask for tips when I'm stumped. =P
It might make sense to add this to the upgrade docs here: http://www.movabletype.org/documentation/mt42/mt-42-upgrade-guide.html as I got bitten by it as well and wouldn't have known to look for issues with that plugin (I'm not even using it!)