You can have your cake and eat it too if you focus on client-side adaptation. For instance, with MIT-licensed Mobify.js which we recently released (http://mobifyjs.com) you can have any amount of mobile-specific functionality while keeping the URL of your desktop site intact. Works especially well if your site is complex!
Used Ticketive for a bit, looks like it could be a solid competitor for Rapportive/GMail itself, especially if third-party developers start contributing functionality.
From what I've been able to find, UIWebViews run as they traditionally have on 4.2, the JS just runs 2x faster exclusively in Mobile Safari, so no performance hit, just no gain either.
From my experience, complicated earn-out structures are a nuisance. They are hard to set up fairly (a lot of edge cases) and even harder to deal with if things go south.
I second what nedwin said about vesting & equal split. Instead of focusing on putting equity value on every hour spent, think of the desired outcome (great company equally split by three cofounders) with a lot of time allocated and a kill switch in place.
PnP model is selling services to startups - first office space, then based on your needs it could be hosting, HR etc. They don't take equity and don't have any limits regarding how long you can stay there (because they get paid cash). However the owner (Saeed) also has a fund and does get in on some Series A rounds. There is a lot more about PnP & Saeed Amidi on thefunded.com
I'd say the VAST majority of sites just plain don't need it. I say that because I read the web all the time on my iPhone and it works just fine. I hardly ever even think about the fact that I'm viewing it on a mobile device, I'm just reading a web page.
Now, for certain sites where there's a benefit, mobile tweaks can be fantastic. But even among the three you list, I've had annoyances. I wish I could remember what it was I was looking for, but I was on google.com on my iPhone the other day looking for something (an app/service from Google itself, I think), and didn't find it in the spot I was used to. I was stumped for a few moments before realizing that I was on the mobile site. Likewise, I've gone to the Facebook mobile site before, trying to do something that wasn't possible from the Facebook iPhone app, and been confronted with the mobile site, which also didn't have the feature I was looking for.
So I guess my feeling is this: while I was initially excited about the idea of mobile-specific sites, I now feel similarly about them as I do about Flash heavy sites: in theory, if everything is executed perfectly, they're fine. But perfection is very rarely achieved, and so it ends up screwing the user up in some unexpected, user-unfriendly way right when you need it not to. So my initial inclination is very much against more "mobile sites" (hey, if it really needs a touch specific interface, an app from the App Store is preferable -- yes, I know I'm being inappropriately iPhone-specific here!), though in favor of small mobile-specific tweaks to normal sites. Changes in font size or moving one column/sidebar somewhere else? Slight interaction changes to make things more appropriate for a tap interface? Sounds great! [And it strikes me that putting these at the level of CMS templates or design frameworks and the like might be the best route.] But a totally different site? Almost never necessary nor even an improvement when it's being used on a sufficiently sophisticated phone (which, they all will be, very very soon).
I know much of this overlaps with what you're talking about and forgive me if I'm being too kneejerk just to the idea of "more mobile-specific sites". It just always stings doubly bad when somebody has poured a ton of work into something that tries to make your life easier but in practice actually makes it harder.
