Though "landing page" is often thrown around in casual conversation to mean "any page a user first lands on," the more precise marketing definition usually refers to a page specifically linked to by an advertisement, the goal of which is to get the user to perform an action such as filling out a form, downloading a file, etc.
Hopefully, almost all Drupal devs and site maintainers are familiar with Drupal's page caching mechanism, but I'll provide a brief high-level overview for the uninitiated and those in need of a refresher:
Page cache overview
Drupal dynamically generates all of its pages, weaving through innumerable hooks, alters, and preprocess functions to finally print out a formatted HTML page. The whole process can be slow and resource intensive, so Drupal offers page caching to mitigate the performance issues.
For all but the simplest of websites, a major version upgrade of Drupal is nothing short of daunting. More than likely, you're currently using modules that don't have stable 7.x releases, or perhaps there's no official upgrade path to the 7.x version. Expect to spend a decent chunk of time "massaging" data through the upgrade process.
We're only halfway through upgrading a very large Drupal 6 site (and I plan a full rundown or series when it's complete), but I have a few nuggets of wisdom that may be valuable to those about to embark on the same journey.
Look, ma! A brand new website built on Drupal 7 using one of them new fancy adaptive themes what makes the website real pretty on those mobile phones. While mostly developer-related (and often Drupal-related specifically), this'll be my primary blogging spot for awhile, and I reckon a few posts completely unrelated to either of those things will make their way in from time to time.
While you're here, you might consider...