Google's announcement yesterday (I learned from the E-mail below) wasn't a shock for most familiar with the app, and keeps up a pattern of Google shutting down apps that don't fit nicely into it's plan for Google + world domination.
I liked Latitude, but the writing was on the wall for some time and I noticed that almost all of the ~ dozen or so of my contacts who were using the app have long-since stopped updating their positions. For me, it was a handy way of collecting history, sharing general location to most friends, and sometimes showing specific location to a few select users, at select times. The API was also useful for developers to extend location functionality into other realms,like Jeffrey Fridel's reverse geocoding functionality for Adobe Lightroom. (which worked mostly, sometimes....
And I hate check-ins: just one more useless "feature" IMHO. I didn't have to check-in w/ Latitude though to still have it be useful for me.
Alternatives? OpenPaths is an altruistic-sounding, privacy-concerned group, that I've tried out somewhat in the past. There are other apps that sound promising on the AppStore, like this one for geotaging photos on non-GPS'd cameras... For me the selling points will be privacy, battery management and functionality related to history. To be continued...