svn's externals work quite well, on the other hand. I know, I know, svn is so 2007, but after fiddling around a bit with git, my impression is that spending time writing code is an order (if not more) of magnitude more important thank screwing around with a version control system, and svn mostly 'just works'. I think that eventually things like git and hg will surpass it, but version control isn't where your startup is going to "make or break" it (unless you're github:-).