Github how? I've yet to see Github being used well for any kind of discussion other than issues.
Three major drawbacks compared to mailing lists: it's on-line, it's proprietary, it sucks for searching and filtering (seriously, the few tools it gives you are a fraction of what you get in any e-mail client).
You have good points; I was commenting on the use as issue tracker which projects seem to do and the use of the actual Google Groups interface. If you use it with an email client that's quite different and yes, you are right there although I don't find it optimal the non proprietary and online nature annoy me too. Maybe I shouldn't use the client and just sign up for the list and respond via email.
Three major drawbacks compared to mailing lists: it's on-line, it's proprietary, it sucks for searching and filtering (seriously, the few tools it gives you are a fraction of what you get in any e-mail client).