Opera’s switch to WebKit means that there are now only three web rendering engines that web developers should worry about rather than four. Certainly there are proponents to this switch, not least Opera itself, but it wasn’t too long ago that this migration and focus towards WebKit had some people concerned. Microsoft appealed to developers in November last year to avoid making WebKit the new IE6. On the other hand, there are those who are not particularly concerned about this shift as WebKit is open source.