A little-heralded feature of iTunes 9.1 is the ability to convert higher bitrate songs to 128kpbs AAC files for iPhone or iPod touch sync with iTunes. How do you do it? It's a simple check box option in the Summary tab when your iPhone appears in the iTunes source list. When the box is checked, on the next sync, all your songs on your iPhone that are not 128kpbs AAC files will be removed and then re-added, being converted on the fly.The first time I did it, about 400 songs on my iPhone needed to be converted. It took about ten minutes to do the conversion. Once the first large conversion is done, the iPhone syncs your music as fast (or slow) as it ever did (unless you're refreshing your iPhone's library every time you sync). If you keep "convert higher bitrate songs to 128kpbs AAC files" checked, any new songs added to your iPhone will automatically be converted.
via tuaw.com

