Difference between jQuery’s .hide() and setting CSS to display: none
From the jQuery page about .hide():
"The matched elements will be hidden immediately, with no animation. This is roughly equivalent to calling .css('display', 'none'), except that the value of the display property is saved in jQuery's data cache so that display can later be restored to its initial value. If an element has a display value of inline, then is hidden and shown, it will once again be displayed inline."
So if it's important that you're able to revert to the previous value of display, you'd better use hide() because that way the previous state is remembered. Apart from that there's no difference.
.hide() stores the previous display property just before setting it to none, so if it wasn't the standard display property for the element you're a bit safer, .show() will use that stored property as what to go back to. So...it does some extra work, but unless you're doing tons of elements, the speed difference should be negligible.
Looking at the jQuery code, this is what happens:
hide: function( speed, easing, callback ) { if ( speed || speed === 0 ) { return this.animate( genFx("hide", 3), speed, easing, callback); } else { for ( var i = 0, j = this.length; i < j; i++ ) { var display = jQuery.css( this[i], "display" ); if ( display !== "none" ) { jQuery.data( this[i], "olddisplay", display ); } } // Set the display of the elements in a second loop // to avoid the constant reflow for ( i = 0; i < j; i++ ) { this[i].style.display = "none"; } return this; }},