I like online sessions better than having to commute to go learn something. They are much more practical and just as lively, rewarding, productive and fun. 

They have a very big disadvantage, though: internet connection and other technical problems.

 I have been doing online classes on skype for a couple of years now, and youre questions are very good. I assumed that its for student learners but I can relate to it as a tutor. I believe so that in the future it will replace physical classes. Annoying things that i experienced having classes on skype are sometimes, the students specially the young learners ,as  you can really tell if they're interested or just being forced by their parents to practice american english. It's like I as a tutor , have been trying to give my best effort when it comes to teaching but on the other way around some students arent theyre not focus and sometimes i hear sounds of games maybe on their phones, thats really frustrating. The entertaining part ... when some students made me laugh about their jokes and sometimes they really try to be funny. ( Im talking about the young learners cause its quite different with adults). About the pj's . yeah i do, most of the time. ;)

a) Well, I've never had a physical classes for learning English, to be honest, so I can't compare them to each other. I think that it's quite a personal thing, for me being in a class with a lot of people is kind of stress, I can't focus on one subject. So, it depends on person, finds he/she this effective or not.  

b) I don't think virtual classes will replace physical, because physical classes help to be socialized with other people a lot. 

c) The most annoying part about it is, like you already said, internet connection. Sometimes I hate my Internet provider. The most entertaining part is being able to talk to people around the world and not even leaving your room, I mean, just think about it - IT'S CRAZY! 

d) :D only PJ's bottom. No one sees it anyway :D 

P.S. sorry for my English, I'm still learning :)

Yea, I do agree that internet connection can be a real pain sometimes. 

I use skype for individuals and groups and it really works well for conversation, pronunciation and discussion. I recommend it for speaking - excellent!