[edit September 2012] Plese also read the updated version for tech issues. It will always have the latest fixes and bugs listed. or, if you got a mobile device, go straight to The iPhone/iPad troubleshooting guide.
There seems to have been made changes to the game that let us collect coins from only one post / person. So you would like to wait for 250/500 coin post until you go and collect.
The best way to get coins right now seems to be by sending hearts to your gaming friends and hope that they send you 100 coin/life back. The problem with this is that some people don’t return this favor, because they get the life even if they use the X to close the dialog and not send you anything back.
There are over 100 inputs in the discussion about collecting coins and the problems with that at the Bubble Witch Saga Fan Site Group at Facebook, please feel free to join us!