I bought the KD-NX5000 for my 300m last summer. Lot of flaws in the unit. Great potential, but so many screw-ups. No idea if the 505 fixes some of this. Anyhow...

Hard Drive: Awesome idea, but damn near impossible to use it. Some idiot at JVC decided that nobody would need to load more than a single album or directory from a CD/DVD onto the HD at one time, so you have to sit there manually copying albums over to the HD. Each album takes about a minute, so you're stuck in your car for hours doing this. The only way to avoid it is to rip all your music to huge single directories on DVD, then copy them en masse. Which sucks if you want to keep your music in albums. Don't underestimate how annoying this is. I bought the 5000 mainly for the HD, so I could avoid buying an iPod, but would up getting the iPod almost immediately after realizing the HD sucked. Also, you can record retail CDs, but only in real-time, which is just as insane.

Navigation: It's good, but the interface is awful. Screen is great, plenty big enough and the graphics are better than the Garmin 350. Just tough to find anything because the interface is based on these terrible radial buttons. Nav is also weird with pulling up POIs, as you seem to have to set the unit for the right town to get them. This is a real ***** in cities with boroughs. I was in Ottawa last week trying to find a mall, but the nav just kept telling me it didn't exist, because I had the unit set on Ottawa and not the borough of Nepean. I think. Anyhow, the interface is a mess. I had my Garmin 350 with me as well, and I found the mall with it in seconds. Oh, and no nav map updates. Contact Navteq they send you to JVC. Contact JVC, they send you to Navteq. Nice support.

iPod Interface: Good controls through the HU, but again, the interface sucks because of those radial wheels. I'm a real tech nut, work in computers, always take to gadgety things right away. But I got screwed up for weeks just figuring out the arcane button presses I needed to load up a playlist and start the music.

Anyways, them's a lot of words to say: Avoid this POS. Awesome potential, but it's all wasted. I had to do it again, I'd get a Kenwood KVT-512 with the nav add-on.