Compare putting the encrypted private key onto some untrusted storage with putting the unencrypted one into an encrypted container like TrueCrypt or LUKS. Technically, the result is pretty much the same, apart from OpenPGP meta data being visible for the encrypted private key.
Your key is as secure as the symmetric encryption algorithm applied for encrypting it using your passphrase. Generally, the algorithms applied are considered secure; given a reasonably long passphrase preventing brute-force attacks is used putting a private key on an untrusted storage must not be an absolute no-go.
But be aware that you're losing a second security net: given the passphrase is cracked/leaked (at any time in future!) or issues with the symmetric encryption algorithm in use are found, you lost the additional security layer of not making the encrypted private key available.
Also consider using OpenPGP smartcards for "sharing" a key between computers and especially subkeys while keeping your private primary key offline (maybe even on a thumb drive usually not connected to your computer). No matter whether you upload the key or not, for sure you've already created a revocation certificate?