I'll get right to it, I can't find enough reasons to use this thing!  I'm going to call it the best home office all-in-one (aka, MFC, Multi-Function Center) printer/scanner/copier/fax money can buy!  Not that I have any experience with other units, so take it for what it's worth, but I've been putting this thing through it's paces over the last week and I couldn't be more satisfied with Brother's MFC-7840W.

Although this unit has built-in wireless capabilities, I chose to hard wire mine using the ethernet port in the back.  It obtained an IP immediately and I haven't had connectivity issues.  The web administration interface is easy to use and I didn't encounter any problems there either.

The Brother software installation was painless on both Windows 7 and Mac OS X (10.5) clients.  Configuration is straight-forward and the software isn't bloated with any junk.  It's lean, unobtrusive, and does what it should.

The print quality is great.  It practically spits out pages and the blacks are dark and crisp.  Copies are quick and simple.  No complaints here.

I haven't tested the fax functionality, so I can't comment there, but the scanning functionality is fantastic.  The automatic tray feeder allows you to insert a stack of papers and simply walk away, very convenient.  The most impressive feature however, is Scan to FTP.  I setup an FTP server (FileZilla) to share a few folders from my file server and the scanner saves them there with the press of a button.  It's made life so much easier!  I come home from work, find a bill in the mail, put it in the scanner and choose scan to ftp.  Seconds later the document is sitting on my network share and I can toss the bill away, no worries.  The quality settings for ftp scans are more limited than a scan using the Brother software, but still quite adequate.  I did a number of tests on speed, quality and file size.  I settled on 300 DPI color scans in PDF format (jpeg is the only other option).  Using the feeder, a single page takes 28 seconds from start to finish and the size averages about 500kB.  Checkout the result below:

Download my Brother MFC-7840W test scan.

Now, I browsed a ton of reviews before making the purchase and the most common complaint I heard was that scans through the feeder were often crooked.  Maybe they didn't bother to adjust the rails; mine have been straight.  A few others mentioned printed pages would curl and that hasn't happened to me either.  Quite a few reviewers said the lights would dim briefly when the thing powered on for a print or a copy and I can confirm that happens to me too.  I'm in an older building, and it hasn't affected anything, so I don't mind in the least.  Overall, it's a great machine.  I recommend it highly.