Should I enable S.M.A.R.T in bios? Pros & cons?

Yes enable it. It would enable logging of the harddisks when errors occurs, and monitors many statistics of the harddrive, such as temperature over time and errors that occur.

Its useful when you use a SMART application inside windows and actually get some useful information, as when you didn't enable it it would not have recorded as much information.

I can' t see any reason not to enable it. Some simple flash devices do not support SMART and may even fail booting because of it. Other than that, i simply wouldn' t know any reason to deactivate it.

I have heard suggestions that it may decrease the overral performance of the hard drive, if ever so slightly.

Is there some general consensus that this should be enabled for pretty much everyone?

I get slightly worried whenever I I'm looking to change from a default BIOS setting. There's a good reason why it's off by default, right?

Just install a SMART application and don't worry about the BIOS setting.
The only thing it does is give you a warning message when the SMART check fails but it won't tell you which parameter failed.

It also enables SMART logging; if you set the BIOS SMART to disabled and do not use any software to enable it right after loading the operating system - it will stay disabled. And that will mean no logs when bad things happen.

SMART is useful - so enable it.  

Although I haven't had any issues with S.M.A.R.T in the past, something very strange happened to me just the other day. My S.M.A.R.T was set to auto in my BIOS, and just after POST, there was a S.M.A.R.T error message which said status BAD, repair or replace hard disk - DEL to continue.

It's a newish Seagate 500GB SATA. When I disabled S.M.A.R.T in my BIOS, my PC boots, but when Windows starts up, before loading any of my startup apps & services, an error dialog appears saying that my hard drive is damaged, and I should backup everything on it and not use my PC until I've repaired or replaced the hard drive.

The strange thing about this whole situation is that my hard drive doesn't make any funny noises or anything. It's quite quiet, and all I hear when I listen really closely is the regular read-sound all hard drives make when it's active.

I've used scandisk on the entire volume and there's no bad sectors or any sort of file system errors on the drive. I'm using Windows 7 Professional. My PC isn't slow in any way and everything still functions as it's supposed to. There's also no read/write errors, so I've ran out of ideas...
Any thoughts from anyone what this could be?

I know this is an old thread - but I came across it, so others may as well... S.M.A.R.T. monitors a number of disk parameters. If it is indicating that the drive is bad, it is beginning to fail - just because this is the case may not mean that you notice an immediate problem such as noise of corrupted files. If in doubt, get the manufacturer's disk monitoring software which will tell you more about the status of the drive. One very useful source is the Ultimate Boot CD:

http://www.ultimatebootcd.com

which has many of the manufacturers utilities, plus a battery of other useful stuff.