E/I domains are very popular formats. In general both are more popular when it is "eWord" or "iWord"
When you get into two words it needs to be something really good, especially with "E"
With "i" domains it is easier to have two word domains since it can be used in several ways. iVerbNoun is a popular format.
Good uses of "e"
eQuotes.com
eHealth.com
Good use of "i"
iSellHouses.com
iAgent.com
iFinance.com