Currently decorated inputs by RadFormDecorator are set with TabIndex="-1", so that they cannot be focused. Expose an additional property in RadFormDecorator through which the decorated button can be focused.

For the time being the focus() can be set to the parentNode of the button. For example:

document.getElementById('Button1').parentNode.focus();

When disabled radiobuttons are decorated by RafFormDecorator they are rendered as enabled in Internet Explorer 11. 
The issue could be worked around by setting "RadioButtons" to the ControlsToSkip attribute of the FormDecorator.

Update: The issue is not observed in Lightweight render mode
Currently text color is different in RadButton (color: #00156E) and decorated ASP Button (color: black) with RadFormDecorator for Office2007 skin. For the time being a custom CSS can be used either for the RadButton or for the decorated ASP Button:

-Custom Styles for the RadFormDecorator:

    <style type="text/css">
        .RadForm_Office2007.rfdButton a.rfdSkinnedButton,
        .RadForm_Office2007.rfdButton input.rfdDecorated[type="button"],
        .RadForm_Office2007.rfdButton input.rfdDecorated[type="reset"],
        .RadForm_Office2007.rfdButton input.rfdDecorated[type="submit"],
        .RadForm_Office2007.rfdButton .rfdSkinnedButton button, 
        .RadForm_Office2007 a.rfdSkinnedButton,
        .RadForm_Office2007 .rfdSkinnedButton button, 
        .RadForm_Office2007 .rfdSkinnedButton input.rfdDecorated,
        .RadForm_Office2007.rfdButton a.rfdSkinnedButton,
        .RadForm_Office2007.rfdButton a.rfdSkinnedButton *
        {
            color: #00156E !important;
        }
    </style>

-Custom Styles for the RadButton:

    <style type="text/css">
        .RadButton_Office2007.rbSkinnedButton,
        .RadButton_Office2007 .rbDecorated,
        .RadButton_Office2007.rbVerticalButton,
        .RadButton_Office2007.rbVerticalButton .rbDecorated,
        .RadButton_Office2007 .rbSplitRight,
        .RadButton_Office2007 .rbSplitLeft
        {
            color: black !important;
        }
    </style>

At present, the MetroTouch scrollbars in the Lightweight RenderMode are dark (almost black). All metro-based skins must have gray scrollbars.

Scrollbars are usually considered part of the browser and users are used to them as they are by default. Thus, using the default browser scrollbars may be the best course of action:

<telerik:RadFormDecorator runat="server" ID="rfd1" RenderMode="Lightweight" ControlsToSkip="Scrollbars" Skin="MetroTouch" />

Alternatively, use a CSS rule like this to unify the metro-based scrolblars (replace MetroTouch with Metro for the Metro skin):

html.RadForm_MetroTouch.rfdScrollBars {
scrollbar-3dlight-color: #cbcbcb;
scrollbar-arrow-color: #787878;
scrollbar-base-color: #787878;
scrollbar-darkshadow-color: #a7a7a7;
scrollbar-face-color: #d5d5d5;
scrollbar-highlight-color: #e6e6e6;
scrollbar-shadow-color: #d5d5d5;
scrollbar-track-color: #f5f5f5; }

Hello.

Would you please concider adding styling of anchor elements to the formdecorator?

It would make it easier styling existing pages.

Tabbing to decorated select element by RadFormDecorator, focuses the original select element. For the time being the following workaround can be used:

JavaScript:

        <script>
            function pageLoad() {
                $ = $telerik.$;
                $.each($(".rfdRealInput"), function (index, value) { value.setAttribute("tabindex", "-1") });
            }
        </script>

ASPX:
        <telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" RenderMode="Lightweight" />
        <asp:TextBox ID="Textbox1" runat="server" />
        <asp:DropDownList ID="Dropdownlist1" runat="server">
            <asp:ListItem Text="text1" />
            <asp:ListItem Text="text2" />
        </asp:DropDownList>
        <asp:TextBox ID="Textbox2" runat="server" />
        <telerik:RadButton ID="RadButton1" runat="server" />

Typing a letter key must move the focus to the next instance of a visible node whose title begins with that printable letter.