As every average geek, I too download torrents (containing only legal, copyright-free material, of course), and most of the time the torrents contain multi-file archives that contain the really juicy data.
A lot of times I return home and find some new torrent has completed downloading, but I have to manually extract the file and wait for THAT to complete.
Well, wait no more!
Through ĀµTorrent's "Run Program" setting (Options>Preferences>Advanced>Run Program), I can execute any command line application I want whenever a torrent completes.
Of course, I use it to execute a PowerShell Script :-D
The actual line I put there is:

powershell.exe -executionPolicy RemoteSigned -file  "%D" "%T" "%N" "%L"

The extra tags at the end are used to pass data to the script - namely the torrent's incoming directory, primary tracker, title and primary label. I keep all of the parameters other than the directory for future use (for example, I may wish to send podcasts automatically into my Kindle-Mail some day).
The script itself only extracts rar files using the GREAT open-source archiver 7zip which has a command line interface, and it goes like this:

param(
[string]$TorrentDir,
[string]$Tracker,
[string]$Title,
[string]$Label
)

"TorrentDir:`t $TorrentDir
Tracker:`t $Tracker
Title:`t`t $Title
Label:`t`t $Label"

# Extract if torrent is composed entirely of rar files into smaller subfolder:
# Check if directory has only rar
$rars = ls $TorrentDir | ?{$_.name -match '\.r(ar|[0-9]{2})$'}
$leadRar = ls $TorrentDir | ?{$_.name -match '\.rar$'}
$nonrars = ls $TorrentDir | ?{$_.name -notmatch '^(Sample(s?)|.+\.r(ar|[0-9]{2})|.+\.sfv|.+\.nfo|folder.jpg)$'}
if((!($nonrars)) -and $leadRar){
    # Directory is release directory
    echo "Extracting"
    $exDir = (mkdir (join-path ($TorrentDir) 'Extracted')).fullname
    $res = &'\Program Files\7-Zip\7z.exe' x "-o$($exDir)" "$($leadRar.fullname)" -y
    if($res | ?{$_ -match 'Everything is Ok'}) {echo "All Good"}
    else {Write-Error "Failed: $res";Read-Host "Press the any key to continue"}
}
else {echo 'nothing here'}

You can see that first it outputs all of the details acquired from ĀµTorrent, checks if the incoming directory has only .rar files (and secondary files, such as .r01), ignoring sample directories, .nfo files etc.
If so, it tells 7zip to extract the primary .rar file into a directory called Extracted.
Hope it helps!