I like the product and as long as they have funding and users I can see them going on to be a player in the market. I don't believe there is not room for a lot of players in the market. They make money from domain name sells as far as I can see.
I do think they are a nice acquisition target for Yahoo or Microsoft, though - both having their own ad networks and no similar offering, it makes a lot of sense for them to buy Weebly and integrate it with their advertising platforms.