Are open source contributions less impressive than personal projects to big companies like Microsoft, Amazon, Google, Facebook, Apple, IBM, etc.?
I assume you're asking this question from a hiring point of view. I can't answer for all those companies, but for Adobe generally, and for my own hiring decisions specifically, absolutely not.
While reviewing résumés, I don't put much weight on personal projects at all, unless they're something that's either super-impressive technically, or they've been very impactful socially or commercially. During the interview stage, talking through a candidate's process regarding their personal project can give really good insights into how they think and work, but the project itself is usually immaterial to this. The exception to that is if the candidate has chosen to do a personal project that's obviously duplicative of something already out there, which often worries me that they'll be predisposed to the Not Invented Here viewpoint and waste my time and money down the road.
Open Source, on the other hand, is a whole other story. It's a world of opportunity from a hiring manager's perspective. You get to see so many things:
- What a candidate chose to work on as an indicator of their interests and motivations
- The actual code that the candidate wrote!
- Assuming it's an established project, how they interacted with others on the project, how they responded to feedback, et cetera. If present, this is probably far and away the most valuable thing.
For Adobe, it's also something that's consistent with one of our core corporate values (Involved), so assuming a candidate is a contributor to a worthwhile open source project, it's a good indicator of cultural fit on their part, as long as they are also comfortable working for a commercial software company and not way out in [copy]left field with RMS and friends.