In addition to the add-on, I have also been using this Unicode keyboard by Keith Stribley. It is really easy compared to old Burmese keyboards where you have to remember Alt keys to type in stacked consonants. An example of stacked consonants would be တ္တ. Now all I have to do to type တ္တ in words like သတ္တဝါ /θaʔ tawa/ is use "`" key to stack တ /t/ below တ /t/. I typed in တ /t/ first and then type တ /t/ again. Then I just type in ` to stack it below the first တ /t/. No more memorizing of Alt keys combinations. Besides, I can also type just like I am writing. For example, ကြ can be typed က+ြ.
Well, I hope that all the operating systems will support Burmese unicode in the near future. I will be interested to see what popular proprietary systems like Zawgyi will do when that happens. Will they adopt the official Unicode or die? There seems to be some people who are trying to migrate Zawgyi to be compatible with Unicode 5.1. I do not know if they are part of official Zawgyi team. However, I wish them good luck for their efforts.