No, it is not a new way to beat the summer heat (my apologies to readers in the southern hemisphere, who may be more interested in a way to stay warm, but this has been a particularly brutal summer here in Philadelphia); it is a frequently reported occurrence in AutoCAD® Architecture 2010 and 2011. Often triggered by the use of the MTEXT command, the freeze occurs if you have more than one CUIX file loaded and two or more each have a contextual ribbon tab (such as the Text Editor tab triggered by the MTEXT or MTEDIT commands) that is triggered by the same command or object selection.
This most frequently happens when both the ACA.cuix and ACAD.cuix files are loaded simultaneously, often so that an ACA user can have access to elements in the ACAD.cuix file that are not part of the ACA.cuix file. Unfortunately, loading both as they are, out-of-the-box, will result in having multiple contextual ribbon tabs for the same triggering action.
The solution is to either not load both at the same time, or, if you must have access to items in both, to create a custom CUIX file that has the items you want from the ACAD.cuix file, but does not have the contextual ribbon tabs (or at least not any that overlap those in the ACA.cuix file). You will need to decide whether it is easier to make a copy of the ACAD.cuix file under another name, and remove the overlapping contextual ribbon tabs -OR- set up a new CUIX file and transfer only the items you want/need from the ACAD.cuix file.