We’ve decided to switch to Symfony2 development in July 2012, if I’m not mistaken - after 7 years of (mostly) Drupal development.
There were reasons to do that:

1. Not-too-great experience with high load projects, powered by Drupal 7

Okay, Drupal is good enough until you get a project with big expectations in terms of response time for authenticated users. Nginx proxy, boost and memcached help a lot with anonymous page hits, but things are sometimes not good enough when we talk about authenticated user saving some nodes (1 field = 2 inserts to fields and revisions table, 40 fields - and you get super-slow node saving, at least on non-ssd hosting), using ajax stuff like dynamic forms (Drupal form ajax is not bad, it’s just not super-blazing-fast).

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