Fermenting in Kegs

I've been brewing beer for about 6 months now. I've done 10 or so batches all together and the last 4 have been all grain recipes rather than extracts. My beer is tasting better with each brew and I'm really starting to get the hang of certain things. I think it's time I start brewing more than 5 gallons at a time to start making it more rewarding. This is what leads me to my question. I've heard of people fermenting in their corny kegs before. Has anyone tried to use the other kind of keg as a carboy? What would the pros and cons of this be? I've taken apart a half barrel before and made a brew kettle out of it, it's something I'm sure a lot of you have done. I don't see why I couldn't dismantle a half barrel, quarter barrel, or even a 6th barrel, attach a blowoff hose and use it like I would a glass carboy. In fact it seems like a great idea, it would come with handles and would be easy to clean because it's stainless steel, and virtually unbreakable. Has anyone tried this? Are there pros and cons? Or should I just stick with glass and buy more carboys?

Plenty of people do it. They actually make an adapter that takes the place of the spear to allow you to use a blow off. You may also be able to use a stopper with an airlock or one of those rubber carboy caps as well. There are also plenty of people who split 10 gal batches between two buckets/carboys/cornys. That might be a cheaper way to get into larger batches while you collect or make more equipment.

I have read about doing this and the biggest con is that you can't see what is clean and what isn't. Also, a lot of commercial kegs have beer stone in them that requires acid to dissolve. I saw a thread on another forum (http://forums.morebeer.com/viewtopic.php?f=15&t=13712&st=0&sk=t&sd=a) about cutting the top off a keg, much like making a kettle and using a gasket and pressure to keep it tight. I have a keg that I have been meaning to turn into this but haven't gotten around to it. Others use a device that attaches to an uncut sanke and provides airlock and transfer tubes but the idea of stuff not being seen and growing freaks me out.

I use a couple of sanke kegs to ferment 10g batches in, one is intact with the ball and ring removed, the other already had the top cut out and I use that one for open ferms. On the un-modified sanke I have a ss fitting with built in racking cane and ferm-lock that attaches to the keg with a triclover latch... can't remember where I got it but it works well. I've seen where guys have made ferm-locks for corny kegs and use them for lagering, but I don't know anyone who uses them for primary. Don't see why it wouldn't work just fine though as long as it's able to vent, otherwise you might have big problems at 150psi or so.

Here's the fitting I was referring to...

http://www.brewershardware.com/Sanke-Fermenter-Kits/

^^ and I as well.