Saturator

Well in metal we have a fairly high floor of noise under the guitar signals anyway, so it's not like we're strangers to it. The tape hiss really depends on the quality of the machine, tape and how well serviced it all is. It only becomes a problem if you're tracking solely to tape and bouncing/compressing a ton. Most people these days will track to tape then bounce to Tools, so you get the best of both worlds.
 
The only audible hiss I can think of hearing is on Black Label Society's Stronger Than Death album. It's always there and really audible on the softer tracks, but can be heard on the heavy tracks as well. It gets really loud on the track Just Killing Time. Kinda cool, but I could probably do with out it. Once I hear it, I focus on it more than the music.
 
Noise and hiss are good, I love it, so I add them instead of cleaning the tracks! But I found that saturating (tried many plugins) heavy guitars usually don´t work for me, it easily start to sound very "digitally" harsh and strange...
 
I'm using saturation plugins almost everyday. Yes, there's exist a lot of cheap saturation plugins which are not really great sonding. I'm in love with sonnex, psp and tritone, and I'm inserting them when I have too digital sounding tracks or just to fattenig and/or warming the tone. And also I can use my inflator for 'virtual headroom' sometimes.
But...
If I have tracks for mixing wich was recorded thru great and maybe vintage preamps to tape then in most cases I will not use any saturators, maybe exept Inflator on very few tracks for even more character.
 
My favourites: Tritone ColorTone, Nebula´s "analog channel" preset, Voxengo Lampthruster and Voxengo Warmifier, also that saturation algorhithm in sonnox limiter is great. I use Inflator too, awesome plugin (but I consider it more like "technical tool" than "warmer")