Dropdowns overhaul:

1. Removed broken and unused dropup examples from the navs/pills docs
2. New defaults for dropdown menus: all corners are rounded and always 1px offset from top unless otherwise specified
3. Refined active and open states for button dropdowns by adding a darker background color for each button variation when opened; also changed the opened dropdown-toggle's inset shadow to match that of an :active button
4. Generalized .dropdown.open to just .open, thus removing a few lines from button-groups.less.
5. Annnnnnnnnd I think that's it.

less/button-groups.less

@@ -114,24 +114,41 @@
 }
 
 .btn-group.open {
-  // IE7's z-index only goes to the nearest positioned ancestor, which would
-  // make the menu appear below buttons that appeared later on the page
-  *z-index: @zindexDropdown;
-
-  // Reposition menu on open and round all corners
-  .dropdown-menu {
-    display: block;
-    margin-top: 1px;
-    .border-radius(5px);
-  }
 
+  // The clickable button for toggling the menu
+  // Remove the gradient and set the same inset shadow as the :active state
   .dropdown-toggle {
     background-image: none;
-    @shadow: inset 0 1px 6px rgba(0,0,0,.15), 0 1px 2px rgba(0,0,0,.05);
+    @shadow: inset 0 2px 4px rgba(0,0,0,.15), 0 1px 2px rgba(0,0,0,.05);
     .box-shadow(@shadow);
   }
+
+  // Keep the hover's background when dropdown is open
+  .btn.dropdown-toggle {
+    background-color: @btnBackgroundHighlight;
+  }
+  .btn-primary.dropdown-toggle {
+    background-color: @btnPrimaryBackgroundHighlight;
+  }
+  .btn-warning.dropdown-toggle {
+    background-color: @btnWarningBackgroundHighlight;
+  }
+  .btn-danger.dropdown-toggle {
+    background-color: @btnDangerBackgroundHighlight;
+  }
+  .btn-success.dropdown-toggle {
+    background-color: @btnSuccessBackgroundHighlight;
+  }
+  .btn-info.dropdown-toggle {
+    background-color: @btnInfoBackgroundHighlight;
+  }
+  .btn-inverse.dropdown-toggle {
+    background-color: @btnInverseBackgroundHighlight;
+  }
 }
 
+
+
 // Reposition the caret
 .btn .caret {
   margin-top: 7px;

less/dropdowns.less

@@ -34,7 +34,7 @@
   margin-left: 2px;
 }
 .dropdown:hover .caret,
-.open.dropdown .caret {
+.open .caret {
   .opacity(100);
 }
 
@@ -49,14 +49,12 @@
   display: none; // none by default, but block on "open" of the menu
   min-width: 160px;
   padding: 4px 0;
-  margin: 0; // override default ul
+  margin: 1px 0 0; // override default ul
   list-style: none;
   background-color: @dropdownBackground;
-  border-color: #ccc;
-  border-color: rgba(0,0,0,.2);
-  border-style: solid;
-  border-width: 1px;
-  .border-radius(0 0 5px 5px);
+  border: 1px solid #ccc;
+  border: 1px solid rgba(0,0,0,.2);
+  .border-radius(5px);
   .box-shadow(0 5px 10px rgba(0,0,0,.2));
   -webkit-background-clip: padding-box;
      -moz-background-clip: padding;
@@ -99,22 +97,18 @@
 
 // Open state for the dropdown
 // ---------------------------
-.dropdown.open {
+.open {
   // IE7's z-index only goes to the nearest positioned ancestor, which would
   // make the menu appear below buttons that appeared later on the page
   *z-index: @zindexDropdown;
 
-  .dropdown-toggle {
-    color: @white;
-    background: #ccc;
-    background: rgba(0,0,0,.3);
-  }
   .dropdown-menu {
     display: block;
   }
 }
 
 // Right aligned dropdowns
+// ---------------------------
 .pull-right .dropdown-menu {
   left: auto;
   right: 0;

less/navbar.less

@@ -262,8 +262,6 @@
 
 // Menu position and menu carets
 .navbar .dropdown-menu {
-  margin-top: 1px;
-  .border-radius(4px);
   &:before {
     content: '';
     display: inline-block;
@@ -304,7 +302,7 @@
 }
 // Dropdown toggle caret
 .navbar .nav .dropdown-toggle .caret,
-.navbar .nav .open.dropdown .caret {
+.navbar .nav .open .caret {
   border-top-color: @white;
   border-bottom-color: @white;
 }

less/navs.less

@@ -98,12 +98,10 @@
 .nav-tabs {
   border-bottom: 1px solid #ddd;
 }
-
 // Make the list-items overlay the bottom border
 .nav-tabs > li {
   margin-bottom: -1px;
 }
-
 // Actual tabs (as links)
 .nav-tabs > li > a {
   padding-top: 8px;
@@ -125,6 +123,7 @@
   cursor: default;
 }
 
+
 // PILLS
 // -----
 
@@ -189,14 +188,11 @@
 // DROPDOWNS
 // ---------
 
-// Position the menu
-.nav-tabs .dropdown-menu,
-.nav-pills .dropdown-menu {
-  margin-top: 1px;
-  border-width: 1px;
+.nav-tabs .dropdown-menu {
+  .border-radius(0 0 5px 5px); // remove the top rounded corners here since there is a hard edge above the menu
 }
 .nav-pills .dropdown-menu {
-  .border-radius(4px);
+  .border-radius(4px); // make rounded corners match the pills
 }
 
 // Default dropdown links