Competing currencies is good for bitcoin.
Currencies compete when they have different properties. Gold and silver do have different physical properties.
The fiat currencies created by central banks have different properties, mostly linked to the economy of the
country that issues them. Peer-to-peer currencies can have different properties too; for example, a Bitcoin
variant with a constant inflation rate would be significantly different from Bitcoin, and would be able to
compete, although I am not sure if it would easily find early adopters.
This is clearly not the case with ixcoin and i0coin; the only difference is in the initial distribution, and a few
cosmetic changes. Therefore, these currencies are merely Bitcoin clones. As such, they need to live in the
same niche as Bitcoin. That is the niche of "digital resource with finite supply that will still be valuable in the future".
It is impossible for two currencies to live in that same niche, because one of them will be perceived as more
likely than the other to hold its future value. People will use that currency for long-term storage of value, and
they will progressively drop the other one. Thus, Bitcoin clones are mutually exclusive. Bitcoin's historical
precedence give it legacy, and strong network effects play for it. It is too late to change that.