Our Sharepoint admin asked me to help him write a script, that found out how much space each DocumentLibrary in our sharepoint farm took up, so after some googeling I found that I could use the StorageManagementInformation Method on the SPSite object, so I cam up with this little script

#First we load the SharePoint assembly
[void][System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")

#Then we create a function that returns tje SPSite
function Get-SPSite($url){
return new-Object Microsoft.SharePoint.SPSite($url)
}

$site = Get-SPSite http://URL
# We use the StorageManagementInformation Method on the $SPSite object, StorageManagementInformation returns a DataTable, and takes 4 input values
# System.Data.DataTable StorageManagementInformation(Microsoft.SharePoint.SPSite+StorageManagementInformationType ltVar, Microsoft.SharePoint.SPSite+StorageManagementSortOrder sordVar, Microsoft.SharePoint.SPSite+StorageManagementSortedOn soVar, System.UInt32 nMaxResults)
#
# ltVar: What kind of storage management information to display
#   List = 1
#   DocumentLibrary = 2
#   Document = 3
# sordVar: the direction in which the items are to be sorted
#   Increasing = 0×10
#   Decreasing = 0×11
# soVar: whether the items are sorted by size or by date
#   Size=0
#   Date = 1
# nMaxResults: the number of results to return

$DT = $site.StorageManagementInformation(2,0x11,0,$(($site.allwebs).count));
$DT | Select @{Label="Size"; Expression={[INT]($_.Size/1MB)}},Directory  | out-gridview
$site.Dispose()

Seems as if I forgot the last line, where I dispose of the Site object, I have added that now.