Here's one quick work-around for entering data in a data entry field when using vncviewer (the alt-tab didn't work for me if the other application covered vncviewer):
1.) Click on an open application that is adjacent to but not covering vncviewer (such as a Tomboy note, which is how I found out the workaround)
2.) Click back on the data entry field of vncviewer; you can then enter data.
I filed recently a duplicate bug (didn't find this thread) at https:/ /bugs.launchpad .net/ubuntu/ +source/ compiz/ +bug/156827.
Here's one quick work-around for entering data in a data entry field when using vncviewer (the alt-tab didn't work for me if the other application covered vncviewer):
1.) Click on an open application that is adjacent to but not covering vncviewer (such as a Tomboy note, which is how I found out the workaround)
2.) Click back on the data entry field of vncviewer; you can then enter data.