Great news for all those folks who rely on Export-Csv and who have been wanting an Append parameter! The latest CTP of PowerShell 3.0 now provides the parameter.
It’s not perfect, but it’s close – if the data you are exporting does not match the current data, you will receive an error:
If you rerun the previous example, with the Force switch, the current directories list of files will be in the “Name” column of the csv file.
If you don’t use the Force, and you DO know what you are doing, this does come in very handy – you can gather data on a daily (or weekly) basis and append it to one file with ease 
Let’s hope Microsoft keeps this in the RTM of PowerShell V3
To get the latest CTP of PowerShell V 3.0, head to the Microsoft Download Center
One note – Don’t forget to uninstall CTP 1 if you have it! I failed to do this, and had to spend quite a bit of time recovering from my inability to read the Instructions.
Unlock-PowerShell 
#1 by jvierra on December 16, 2011 - 19:56
Isn’t it great – these PosH guys really rock!
#2 by Karl Mitschke on December 20, 2011 - 11:24
Yes, it’s great!
There are more enhancements as well, which I hope to write about.
#3 by Karl M. on March 4, 2012 - 17:04
Does it do a better job of leaving out unnecessary quotes or does it still cram them in everywhere?
#4 by Karl Mitschke on March 5, 2012 - 14:35
I guess that depends onyur definition of “unnecessary quotes” – if you give me an example I can test it.