I'll be arriving in the Johannesburg airport and I've been told to take a kombi from there to [somewhere where they have kombis to Swaziland] and then from there to Mbabane. Does anybody have experience with this?
Not kombi vans exactly, but Go Swaziland offers comfortable-looking minibus transport from Johannesburg direct to Mbabane, meaning you won't have to figure out how to change in the middle in some other town. They'll also stay with you through the border crossing.
There was a kombi from the airport to Swaziland (Mbabane and Manzini) for 400 rand