JRuby's startup speed isn't that much different if you're actually running something fairly heavy, like a web framework; it's not like Rails starts up in 200ms on MRI and 4000ms on JRuby, both have you waiting for a few seconds. With source reloading they're not that different in practice.
Sure, leaner RAM consumption is nice, but so is stable RAM consumption. It's not uncommon to see a Rails app on MRI eventually grow from, say, 70MB to 300MB+ and never shrink thanks to heap fragmentation and gc confusion, while JRuby stabilizes at maybe 100MB.
Sure, I also have MRI services which sit stable at 8-15MB for 6 months or more and JRuby's not exactly going to help there, and for short running interactive tasks it's certainly not going to be my first choice, but having the choice is very, very good.
Sure, leaner RAM consumption is nice, but so is stable RAM consumption. It's not uncommon to see a Rails app on MRI eventually grow from, say, 70MB to 300MB+ and never shrink thanks to heap fragmentation and gc confusion, while JRuby stabilizes at maybe 100MB.
Sure, I also have MRI services which sit stable at 8-15MB for 6 months or more and JRuby's not exactly going to help there, and for short running interactive tasks it's certainly not going to be my first choice, but having the choice is very, very good.