SBMたくさん購読してると:saするのが面倒なので

// ==UserScript==
// @name        ldr_add_thumbnail_sbm
// @namespace   http://d.hatena.ne.jp/tnx/
// @include     http://reader.livedoor.com/reader/
// @version     1.0
// ==/UserScript==
// based on http://la.ma.la/misc/userjs/ldr_add_thumbnail.user.js

(function(){
    var w = unsafeWindow;
    var pat = new RegExp("^http://(b\.hatena\.ne\.jp|del\.icio\.us|1470\.net/mm/)", "i");

    w.register_hook("before_printfeed",function(feed){
        if(!feed.filtered_simpleapi && pat.test(feed.channel.link)){
            feed.items.forEach(function(item){
                var url = item.link;
                item.body = [
                    '<img src="',
                    'http://img.simpleapi.net/small/',
                    url,'" align="left" style="margin:8px">',
                    item.body,
                    '<br clear="both">'
                ].join("");
            });
            feed.filtered_simpleapi = true;
        }
    });
})();

SEE ALSO

http://la.ma.la/blog/diary_200605242222.htm