Most of my contacts are in LinkedIn, but you can't store phones numbers, IM addresses, etc, there. The vast majority of my phone contacts are in my cell phone, but those die every time I kill a phone, which is about every 3-6 months these days. I used to use Yahoo Mail contacts, but since I couldn't get that contact list to sync with my phone it stopped being useful. GMail contacts are generally fairly useless as well.
So here we go again. New phone, new contact I need to store, where do I put it? Plaxo seems like a reasonable solution, but I remember bad creepy stuff from them a few years ago so I'm hesitant to jump back in with that.
I'm thinking a system where you can express relationships, ala LinkedIn or FaceBook, and contact details are published and maintained by the person you know (as opposed to you) is a good thing. Combine this with the FriendFeed / Venturehacks Recommended model where you can create entries for people that are not on the network yet, and allow syncing with phone or otherwise make it always-available, and you got something good. Also will need the ability to identify contacts as personal, business, etc.
What do you use, and do you like it?