boom!!! Here is a hack solution to make atom start faster. For Atom <= v0.170.0

atom.js

     Atom.prototype.startEditorWindow = function() {
      var CommandInstaller, dimensions, maximize, resourcePath, safeMode, _ref;
      _ref = this.getLoadSettings(), resourcePath = _ref.resourcePath, safeMode = _ref.safeMode;
      CommandInstaller = require('./command-installer');
      CommandInstaller.installAtomCommand(resourcePath, false, function(error) {
        if (error != null) {
          return console.warn(error.message);
        }
      });
      CommandInstaller.installApmCommand(resourcePath, false, function(error) {
        if (error != null) {
          return console.warn(error.message);
        }
      });
      dimensions = this.restoreWindowDimensions();
      // this.loadConfig();    
      this.themes.loadBaseStylesheets();
      this.keymaps.loadBundledKeymaps();

      setImmediate((function(_this) {
        return function() {
          _this.deserializeEditorWindow();
          _this.themes.activatePackages();
          _this.packages.activatePackage("tabs");
          _this.packages.activatePackage("status-bar");
          _this.packages.activatePackage("tree-view");
          
          _this.loadConfig();
          setTimeout(function(){
            _this.packages.loadPackages();
            _this.watchProjectPath();
            _this.packages.activate();
            _this.keymaps.loadUserKeymap();
            if (!safeMode) {
              _this.requireUserInitScript();
            }
            _this.menu.update();
            _this.subscribe(_this.config.onDidChange('core.autoHideMenuBar', (function(_this) {
              return function(_arg) {
                var newValue;
                newValue = _arg.newValue;
                return _this.setAutoHideMenuBar(newValue);
              };
            })(_this)));
            if (_this.config.get('core.autoHideMenuBar')) {
              _this.setAutoHideMenuBar(true);
            }
          }, 200); //NOTE: here can change
        };
      })(this));

      // this.packages.loadPackages();
      // this.deserializeEditorWindow();
      // this.watchProjectPath();
      // this.packages.activate();
      // this.keymaps.loadUserKeymap();
      // if (!safeMode) {
      //   this.requireUserInitScript();
      // }
      // this.menu.update();
      // this.subscribe(this.config.onDidChange('core.autoHideMenuBar', (function(_this) {
      //   return function(_arg) {
      //     var newValue;
      //     newValue = _arg.newValue;
      //     return _this.setAutoHideMenuBar(newValue);
      //   };
      // })(this)));
      // if (this.config.get('core.autoHideMenuBar')) {
      //   this.setAutoHideMenuBar(true);
      // }
      maximize = (dimensions != null ? dimensions.maximized : void 0) && process.platform !== 'darwin';
      return this.displayWindow({
        maximize: maximize
      });
    };

After discuss in why-is-atom-so-slow, I pull a request Better user experience for start atom: atom/atom#4269.

Today, I do a deep review the atom source code, and find a hack solution to make atom start faster:
this is the final modify screen video demo:
https://drive.google.com/file/d/0B8i7zRr2bfCAV0NoeG50dURMaW8/view?usp=sharing

What It Is

It delay the config file load, and the packages load and active, which cost much time on start.
After change, atom only load and active the must packages on start, which is ui theme、syntax theme、tabs、status-bar、tree-view.
Then delay to load and active other package. Window and mainly package will show quickly.

How To Do:

1、open atom.js
for mac: /Applications/Atom.app/Contents/Resources/app/src/atom.js
for win8:

C:\ProgramData\chocolatey\lib\Atom.{replace to atom version}\tools\Atom\resources\app\src\atom.js  

2、replace the below function Atom.prototype.startEditorWindow
3、you can test and change the setTimeout time to adapt your computer.
4、notice that you should modify atom.js again after you update the atom.

For atom v0.192

    Atom.prototype.startEditorWindow = function() {
      var CommandInstaller, dimensions, maximize, resourcePath, safeMode, _ref3;
      _ref3 = this.getLoadSettings(), resourcePath = _ref3.resourcePath, safeMode = _ref3.safeMode;

      CommandInstaller = require('./command-installer');
      CommandInstaller.installAtomCommand(resourcePath, false, function(error) {
        if (error != null) {
          return console.warn(error.message);
        }
      });
      CommandInstaller.installApmCommand(resourcePath, false, function(error) {
        if (error != null) {
          return console.warn(error.message);
        }
      });

      dimensions = this.restoreWindowDimensions(); // 18ms
      this.loadConfig(); // 9ms
      this.keymaps.loadBundledKeymaps(); // 8ms
      this.themes.loadBaseStylesheets(); // 29ms

      this.themes.activatePackages();
      this.deserializeEditorWindow(); // 161ms
      setImmediate((function(_this) {
        return function() {

          _this.packages.activatePackage("tabs"); //50ms
          _this.packages.activatePackage("status-bar");//24ms
          _this.packages.activatePackage("tree-view");//18ms

          setTimeout(function(){
            _this.packages.loadPackages(); // 210ms
            _this.watchProjectPath();
            _this.packages.activate(); // 309ms
            _this.keymaps.loadUserKeymap();

            if (!safeMode) {
              _this.requireUserInitScript();
            }

            _this.menu.update();
            _this.disposables.add(_this.config.onDidChange('core.autoHideMenuBar', (function(_this) {
              return function(_arg) {
                var newValue;
                newValue = _arg.newValue;
                return _this.setAutoHideMenuBar(newValue);
              };
            })(_this)));

            if (_this.config.get('core.autoHideMenuBar')) {
              _this.setAutoHideMenuBar(true);
            }
            _this.openInitialEmptyEditorIfNecessary(); // 8ms
          }, 100);

        };
      })(this));

      maximize = (dimensions != null ? dimensions.maximized : void 0) && process.platform !== 'darwin';
      return this.displayWindow({
        maximize: maximize
      });
    };

The Path on Mac isn't exist, can you update it please?