This tongue in cheek post by Dion about Ruby not scaling made me chuckle but also got me thinking!
The whole question of whether a modern language scales or not is really the wrong question to ask. Almost any language will scale horizontally. Here’s one anecdote as an example: when we were going through the language selection process at GreatSchools several years back we rewrote some key pages in PHP, Java, and Perl (mod_perl) to try them out. Not surprisingly we found that under load test all of the solutions scaled within 5 percent of each other after some tweaking.
Over the years I’ve faced scalability issues with Perl, PHP, and Java in companies getting close to outgrowing their data centers and regardless of language we’ve always attacked the problem successfully from the same 3 points: database optimization, session handling approach, and page/fragment/dbresult caching. The bottom line of scalability is that it’s all in how you write and architect your application and not which language you use! Will Java/Ruby/C#/Perl/Python/etc scale? Of course they will and when they don’t it’s usually the application that’s the problem and not the language.
Given that salaries are MUCH more expensive than hardware I no longer worry about whether a language will scale. The real question is how productive people will be in the language and even that is really a question of available higher level frameworks than of language.