Cetti and Clanad, (on the link above), seem to have covered the whole topic extremely well.
I am not an expert in this area but I have just two observations.
1) A pastor whom I respect immensely, describes himself as a, "moderate pentecostal," and believes in speaking in tongues. I presume from this, that he has experienced this himself.
2) This same pastor warns against what is known as, "the Toronto Experience," whereby people supposedly filled with the Holy Spirit, become babbling idiots, making animal noises, and falling about in uncontrolled laughter.
This apparently demonic possession, a deciet for the real thing. The Alpha courses culminate in a, "Holy Spirit weekend," where this phenomena is passed on to the "students." I have no personal experience of this, but am reliably informed that this is so.
Some of the "Televangelists," do this in front of the camera, ("God cahannel"), and I find what I have seen ridiculous and unedifying.