In a way, Perforce is a cute middle ground. It has "pending changelists" that ReviewBoard or Phabricator can slurp up and present to reviewers. You can easily give another person your changes by "shelving" them. Mutable history is only really a "feature" in tiny projects; in massive ones, immutability simplifies life greatly and restores peace of mind. In many ways, the way Perforce handles conflicts is nicer: it doesn't pollute the actual files with conflict markers, and has an option to resolve conflicts in a nice 3-pane UI. Although it does get merges wrong every now and then.
Non-linear history is considered an "anti-feature" by many, and the LLVM community runs a primary SVN server; users submit via git-svn.
Having cheap and lightweight branching is what leads to merge headaches. In fact, (from one Tech Talk), I believe that Google runs a single branch to evade merge problems altogether.
I think git's greatest asset is the excellent local development experience. You can muck around as much as you like, making local branches/commits as checkpoints, and squash them in to submit a final patch. The command-line UI is fantastic, and everything is snappy (provided you have a small checkout). I think having a single linear "trunk" on the server-side is a good idea.