On a) - cool is very subjective, so perhaps there's no point in even mentioning it. It depends on the person you ask.
On point b) - Facebook is focusing on making it's services more useful to business, at the detriment of it's core users. Facebook became popular in Harvard because you could scope out that cute undergrad you spotted around campus. The people in your network were tied to your friends and classmates in the real world. The more Facebook grows, the more it devalues it's definition of 'friend' (Facebook's definition of friend that is. Having 300 Mafia Wars friends might make me spend more time on Facebook for a while - increasing Facebook's stickiness, hence it's value to brand advertisers, but it doesn't mean I'll ever have a meaningful interaction with the members of my "Mafia").
Do I want to get notifications every time a 'friend' of mine 'likes' Xbox Live? No. That's not a real interaction - it's just spam. Do I want a notification every time a friend of mine logs into their account in a Starbucks (this is how I'd imagine their location-based feature working)? No. Of course I don't. I want my social network to only give me message that aren't auto-generated, i.e. those that are real messages from real people. Like HN comments.
I think Facebook has forgotten about what made it popular in the first place, and now because of it's size and self-sustaining growth, will implement features that are useless to it's core user base. There will be no telltale indicators (at least externally) of this growing dissatisfaction because any attrition of it's user base will be compensated by new, incoming users. And of course many people who don't like the service will hang around because they don't want to be out of the loop.
What I envision as the ideal would be social networks to emulate email and SMS. I can send a Gmail email to my Hotmail based friend. If I don't like Gmail, I can switch email providers and take my contacts with me. Social networks should organise in 'tribes'. You associate with whatever tribe you feel describes you best. Tribes can interact with each other. If I don't like my tribe (perhaps because it's becoming MySpace-like) I can move easily to another. There could be a tribe that appeals to HN type users, and another for 12 year old girls, and another for retirees. Each have their own identity and values. What I'm describing is an open protocol for social networks, which forces "tribes" (individual networks) to compete on how good they are, rather than how many of your friends are on that particular network. This will keep them honest as they can't depend on user lock-in. In an ideal world, Diaspora and Facebook would be on an open protocol and users could switch easily and painlessly.