Sure it will be. Just look what Google does on the market. He is making small applications (calendar, pictures, reader, mail), which together makes one big application.
Sites is just a piece of this bigger application. Connecting notes from notebook, adding pictures from Picasa album,...
it's Google baby.
I wouldn't be so sure in Apple. At last, he is "product" company, and I think that iTunes is only his side product. But, in other way, people who like Apple, or have iPod, iPhone, use iTunes a lot...
FF has great and big community support (extensions, translations, etc.) but on other side IE has large support from gov. big monopolists.
I think facebookmail.com is well enough good.
Sites is just a piece of this bigger application. Connecting notes from notebook, adding pictures from Picasa album,...
it's Google baby.