Had TomTom on my PDA, but I've now got CoPilot 8 Live on my iPhone.
Only had it a few days, but so far, it's fantastic. MUCH better definition than TomTom.
Will be doing some long trips over the next couple of weeks, so will be able to test it in a bit more depth. But for £25 (compared to £60 for TomTom)
AND £150-odd for a hardware satnav.....
Haven't changed the HU from the RCD300

YET, but I'll probably get either a compatable iphone stereo, or something with a Hard Drive (not RNS510 though - waste of money imho)
Dan