Awhile back Yahoo! positioned itself as a "life engine" - it was a nice way of saying "we're a portal". I really liked the notion given all they do and the fact I rarely used them for search but did use them for email, finance, news and all kinds of other things.
Google, for me, equals search - something they seem to agree with. And therein is the problem as they launch all kinds of other services. I like Gmail for random storage of all kinds of things. But as far as email goes I have my own address and prefer the interface of the new Yahoo mail. I use Spotlight and MS Search on my respective notebooks for finding addresses and long-filed-away emails in a rush and deleted Google desktop sometime ago. Where Google wins is on stuff like Maps - but only due to the fact I really understand their maps - there is no stickiness for me.
All this points to the positioning challenge Google faces as it tries to become more things to more people. Nicholas Carr gets at this in a recent post.
Google has us trained to think of it as synonymous with "search." That's been good for the company up to now, but such a narrowly drawn identity may well be a hindrance as Google moves into ever more lines of business. Yahoo's less well-defined identity has hurt it in competing for search traffic with Google, but it helps it in promoting a range of other services... You can't be more than Mr. Spock if Mr. Spock is all you really want to be.