The change to px seems the right thing. The text remains sharp, even if enlarged by Ctrl+. In the current stable version of VSD the text became pixelated and unsharp if enlarged many times.
As to overlapping: In FireFox, if the text box you draw in VSD has some extra space on the right side, you can enlarge a lot before it starts wrapping. But if the text box is just as wide as your text, it will wrap, and text boxes below each other will overlap if enlarged beyond a certain point. The page width remains the same because of the wrapping.
In the other browsers I tested (IE, Safari, Opera, Chrome, all latest stable versions) the text did not wrap nor overlap, even though the drawn text box was exactly fitting around the text. But the page width was increased because everything was pushed to the right when enlarging.
For this test I scaled up the text quite a lot (and in Opera it seems you can go on forever). In real life I don't know if such a lot of scaling will ever be necessary.
In all five browsers I tested with some text and a shape it displayed exactly the same. Even in Chrome, which usually renders things a bit larger than the other browsers.
I tested the new version on my desktop pc (win7/64) while having the current stable version on my laptop (Vista) for comparison.