we have been going through the migration process for approx 18 months now and all of the hurdles have been jumped and the fees paid.  The money has been taken from our account for the medical bond but we have been waiting 4 weeks for the visa to come through: is this normal??  Obviously we are getting very frustrated as home, car etc all sold this end!!! just waiting to buy flight ticket.

Hi Stephen,
You probably refer to the Assurance of Support bond. It is normal to take a long time between lodgment of the bond and visa grant. It is best if you let your case officer know that the bond has been lodged and email a scanned copy of the receipt. This may speed up the process a little. Also check the dates of your police clearances and medicals. Most of those documents are only valid for 12 months. Your application has been pending for 18 months. You may check if a request for new set of those documents is coming.
Dessie