Lightroom works quite well considering that it has to deal with large files and keep them all organized. Nevertheless it can become really slow when working with large albums. All these problems magically disappeared when I switched my Lightroom work from a 2007 MacBook Pro to a Quadcore 16GB PC — I really wonder why? One thing that still bothered me was the constant “Loading…” message when browsing pictures. Especially when you’re selecting photos to delete, it gets very annoying to wait for the pictures to become fully loaded.
The remedy is to activate prerendering of the previews on import. You can find it in the import dialog on the right side “Render Previews”: Select “Standard” here.
If you’ve already imported the album select all photos and choose Library -> Previews -> Render Standard-Sized Previews. The 1:1 Previews are used when you zoom in 100% by clicking the picture when the loupe cursor is displayed. I don’t do this very often and haven’t activated the option yet. Rendering the previews for the images sure requires some extra space on your hard disk but the advantage is to big, I think it’s a very good trade-off.