So I had a go. It's interesting, it seems like it could be useful but it's not really going "Here's some Ruby stuff that's useful on a daily basis" and it's more copy this line as well as you can in 10 minutes. It might help with muscle memory learning, but I didn't feel it helped get my brain anymore Ruby geared. YMMV.
I had a similar experience with actual push-ups: I did a few one day, didn't feel like it helped, and dismissed the whole idea.
Ah notice how I'm carefully saying I didn't think it helped my learning, not that it was useless. Some people probably wouldn't find pushups as useful in their exercise routines as others ;)
I think it's more that being very precise/quick typing keywords isn't really the same in any way as 'practicing programming thinking'