I haven't tried it. The place I live is not sufficiently trendy for this substance (clearly ripe for abuse) to have arrived yet. I'm sure it will soon be available even here, though. Someday, it will be sold at Safeway.
This is the invasion of the tapioca-laced tea about which the book of Revelations should have told us!
Be on guard! All the indications are that you will experience bubble tea sometime soon!