I acquired a Yubikey Neo last month. Now I want to use the Smart-Card functionality for PGP. I followed the official guides on the Yubico Website tested it with 2048 RSA Keys and it worked fine. But if I would lose the Key I would have a Problem, because the main private key was solely stored on the Yubikey. So I tried another approach. I created a key on my Computer and used it to generate three subkeys, one for signing, one for authentication and one for encryption. Then I moved the three subkeys on the Yubikey. I wanted to store my Master Key in a safe place and wanted the Yubikey for daily use. I used RSA 4096 for my Master key and RSA 2048 for the subkeys because the Yubikey does not support greater keys. This worked as well.
GPG supports ECC in newer versions. Is it possible to create a Master key using ECC instead of RSA (Subkeys would still be RSA) and will I be able to communicate with other people (using my subkeys) who use systems that don't yet support ECC? And will they be able to sign my Key and I theirs without problems?