I know the original question was posted back in 2007, but I'm still finding other Perl forums with a similar question. I just came across this very same problem with Perl 5.8.9 for WIndows from ActiveState. Previous answers in the comments are correct, but perhaps not entirely clear to some programmers (please refrain from follow up comments about real programmers, etc). To help others with this problem today and in the future, here is exactly what I did.

Near the top of my script I added the suggested ENV line:

$ENV(HOME) = "C:\\Perl\\myscripts\\etc";

This setting tells the script where to save your SHH settings. Run your script after that, and assuming no other problems are present, you'll see a directory named .shh in the directory you specified with the $ENV(HOME) setting. Look in that directory and you should find a file named something like known_hosts2. If you have all that, then you've solved the getpwuid function problem (and a few other related problems I'm guessing).

After setting that variable I was able to connect to an SFTP server and download a small file; however, the Net-Sftp page on cpan says that when you call "get" to retrieve a file that the $localfile setting is optional. I found that was not the case. I had to spell out completely the remote file I wanted and what I wanted to call it once it downloaded. Here's an example:

$remotefile = '/home/joe_user/addresses.txt';
$localfile = "C:\\temp\\addresses.txt";
$sftp->get($remotefile, $localfile);
[download]

When I didn't include the $localfile setting, I didn't get anything. Actually, I downloaded the file but it was never saved to any place I could fine. I know that was a simple illustration for most of the experienced Perl programmers that frequent this forum; however, for the casual Perl programmer, I probably just saved them a big headache. Enjoy and thanks to the previous comments that contained the solution. I only posted to add further clarity in hopes to help out others.