I keep my right hand fingernails a little bit long, in order to facilitate playing classical and jazz. Left hand nails are kept short enough to stay out of the way completely.

Originally Posted by: Itsmesilly
is the sound just not as crisp clean and clear?

That and, more importantly to me, is the accuracy and precision that is only possible with a fingernail as opposed to the rounded, softer flesh of your fingertip.

I can easily "dial back" my attack in order to get a softer, muted sound when desired. But without the nails I can't get up to that certain level of speed, clarity and precision.

I discuss fingernails in the first lesson of this tutorial aimed at classical right hand technique:

http://www.guitartricks.com/tutorial.php?input=324

In this one (and others) you can see I am using my nails to achieve blues:

http://www.guitartricks.com/tutorial.php?input=151

And in most of my jazz lessons I use fingerstyle exclusively. For example:

http://www.guitartricks.com/tutorial.php?input=644
http://www.guitartricks.com/tutorial.php?input=708

Quite often I use my index or middle finger as if it were a pick. Hope this helps!