CSS-only multi-line ellipsis with generated content. License: http://www.wtfpl.net/txt/copying/

gistfile1.scss

@import "compass/css3/images";

// CSS-only multi-line ellipsis with generated content
// yields `position:relative`, so remember to declare an eventual `position:absolute/fixed` *after* including this mixin
@mixin limitLines(
    $maxLinesPortrait, // Mandatory: The number of lines after which the clipping should take action.
    $maxLinesLandscape: $maxLinesPortrait, // You may provide a different line limit for landscape orientation.
        // Note that 'portrait' is our default orientation. However, if you omit $maxLinesLandscape,
        // the value of $maxLinesPortrait is used for whatever orientation (that is, without a media query).

    $fgCol: #000, // Set this to the color of the text element you want to clip.
    $bgCol: #fff, // Set this to the background color of the text element you want to clip.
    $lineHeight: 1.3 // Provide the (unitless!) line-height of the text element to help position the ellipsis correctly.
) {
    position: relative;
    overflow: hidden;

    // root element class added via JS feature detection
    .webkit-line-clamp & {
        text-overflow: ellipsis;
        display: -webkit-box;
        -webkit-box-orient: vertical;

        // always remember:
        // http://alistapart.com/article/every-time-you-call-a-proprietary-feature-css3-a-kitten-dies
        -webkit-line-clamp: $maxLinesPortrait;

        @if($maxLinesLandscape != $maxLinesPortrait) {
            @media screen and (orientation:landscape) {
                -webkit-line-clamp: $maxLinesLandscape;
            }
        }
    }

    html:not(.webkit-line-clamp) & {
        max-height: $maxLinesPortrait * $lineHeight * 1em;

        // Pseudo-element containing the ellipsis (see below)
        &::before {
            top: ($maxLinesPortrait - 1) * $lineHeight * 1em;
        }

        @if($maxLinesLandscape != $maxLinesPortrait) {
            @media screen and (orientation:landscape) {
                max-height: $maxLinesLandscape * $lineHeight * 1em;

                &::before {
                    top: ($maxLinesLandscape - 1) * $lineHeight * 1em;
                }
            }
        }

        // Pseudo-element containing the ellipsis, as well as a soft gradient to make in-word ellipses look less harsh.
        &::before {
            @extend %limit-lines-ellipsis;
            color: transparentize($fgCol, 0.7);
                // No -ms- support in Compass? Strange!
                background: -ms-linear-gradient(left, transparentize($bgCol, 1), $bgCol 2em);
            @include background(linear-gradient(left, transparentize($bgCol, 1), $bgCol 2em));
        }

        &::after {
            @extend %limit-lines-filler;
            background: $bgCol;
        }
    }
}

// The ellipsis itself.
// Fine-tune the balance between text clipped a bit too early vs. the probability of slightly orphaned ellipses
// via the min-width property: Higher = text clipped earlier, less orphaned ellipses. And vice versa.
%limit-lines-ellipsis {
    min-width: 25%;
    content: "…";
    position: absolute;
    right: 0;
    padding-left: 2em; // for the gradient
}

// Pseudo-element containing a good amount of whitespace.
// This is appended to the text to be clipped, in order to overlay (and thus hide) a superfluous ellipsis
// occurring when the text fits exactly into the number of lines specified.
%limit-lines-filler {
    // generate a good amount of alternating normal spaces and non-breaking spaces
    $whitespace: "";
    @for $i from 1 through 1024 {
        $whitespace: $whitespace + "  ";
    }
    content: $whitespace;
    display: inline;
    letter-spacing: 1em;
    position: relative;
    z-index: 1;
    // make this a bit smaller to avoid cropping of descenders from the line above
    font-size: 75%;
};

gistfile2.js

if (typeof window.document.createElement('div').style.webkitLineClamp !== 'undefined') {
    document.querySelector('html').classList.add('webkit-line-clamp');
}

Sample usage:

@include limitLines(
    $maxLinesPortrait: 3,
    $maxLinesLandscape: 6,
    $fgCol: #000,
    $bgCol: #fff,
    $lineHeight: 1.3
);