Earlier quoted context omitted.
It's definitely noticably slower, but 4 seconds per startup would make it unusable for me. However, since it's time jruby -e 1 real 0m0.514s user 0m0.510s sys 0m0.040s I find it acceptable (could it be the SSD in my laptop that makes such a large difference?). As http://jira.codehaus.org/browse/JRUBY-5181 shows, as soon as some gems come into the picture, actual startup times deteriorate rapidly.
I'm not an SSD, but mine was also a cold start; are you sure yours wasn't already cached?
I don't reboot that often, so it took me a while before I could try it, but my home desktop, also with SSD, gives
user@twen:~/tmp$ time jruby -e '1'
real 0m0.664s
user 0m0.390s
sys 0m0.110s