You can group polygons by colorizing them. Select any number of polygons and press 'C'' or click on colorize button. Select color. Display world in polygon color mode to check colorization effect. Double click will select all nearby polygons with same color. You can also select all polygons with same texture on active texture layer with Ctrl+LMBx2. You can select adjacent polygons with same texture with Ctrl+RMBx2. Ctrl+Shift+LMBx2 will select all polygons with same color in sector. Ctrl+Shift+RMBx2 will select all polygons with same texture in sector. In you right click on texture in browser you can choose to select all polygons with current texture in world. There is also ability to select polygons in world that don't contain any of selected textures in browser. You can also add all textures from world into browser.