EDIT: I have subsequently learned about git merge --no-ff and no longer re-parent. But I'll leave this up in case someone finds it useful anyway.
I'm not a command-line person, I may have grown up with it but... let's just say I've developed an allergy. I want GUIs, I want simplicity and I want visual corroboration that I'm doing what I think I'm doing. I really don't see why I need to become an expert in every tool I use before it can be functional.
This is why I adore SourceTree, and (last time I used it) GitEye. Easier, more intuitive interface, and visualizations to help you see whether what you're doing makes sense. You're less likely to make mistakes!
I'm also (and for similar reasons) a huge fan of squashed merges in Git; one commit per feature / bugfix / hotfix, and (theoretically) the ability to go through the individual commits on my own time if I ever need to. I use interactive rebasing* a lot to achieve a similar result, but getting other devs to use it responsibly is a lot more trouble than teaching them to add --squashed to the merge command. The downside is that because I've become used to interactive rebasing to squash my commits before merging, I've also become used to using regular merges and seeing a neat line on the branch graph showing me where my merges originated. Squashed commits don't give you that. And that's sad. It's also problematic - this morning I freaked out because I thought the code in a branch I'd squash-merged into wasn't where it needed to be, all because I was relying on those parenting lines and didn't immediately think to do a diff**.
* Ironically, from the command-line. It's the one thing I find less intuitive and more risky using SourceTree.
** While we're talking about branch diffs, if you're using Bitbucket don't trust the branch diff - the UI uses a three-dot diff and what you actually want is a two-dot, ie git diff branch1..branch2
So, after much surfing around the internets and learning lots more about git's inner workings than I care to, I came across an elegant little solution and have wrapped it with a bash script in the hopes that it'll be found useful. All you have to do is run this script as follows:
./add_parent.sh TARGET_COMMIT_ID NEW_PARENT_COMMIT_ID