Yep I've had the same problems with exporting ai format as text.

Normally I just play around with settings until it exports right. But I have just had another go and have found some possible text bugs in Xara that at first look might be the problem.

I went back to have a look at some text that originally had problems. I highlighted the whole text object with the text tool and the font was Arial, size 12pt. But I had some empty carriage returns at the end of the text and on cursoring down to the end the font and size changed. Even if I highlighted the whole text and changed font/sizes etc the empty carriage return stayed at different settings. I deleted the extra carriage returns and there was still a problem, then I entered them again and found that the text change was still being remembered somehow.

I think originally the different text was caused by typing in the standard Times Roman then I selected the whole text with text tool and changed it to Arial etc. The text object had empty carriage returns on the end and the end one stayed as Times.

The way I found around this was to click with the text tool on the page background and select the text with the selector tool and then click back on the text tool and set font and sizes etc. Then the whole text object was back to normal and exported okay. I think that sometimes there are invisible text settings in Xara that cause what Illustrator calls 'illegal operands'.

Even after all this some of my fonts get replaced in Illustrator for some reason, not sure why.

I've just had another go and found some inconsistencies with this, as sometimes a change in text in an empty carriage return causes a problem and sometimes not, weird. So still a bit confused as to what is actually the problem

Anyway hope this helps.

Regards

Su