The main feature of gold is performance: It's much more efficient than the old binutils ld, and it is multithreaded (given that linking is not an immediately obvious source of low-hanging parallelism, this is an interesting case-study). Ian compares the performance of gold and ld when linking a “900M C++ executable”. Ian works for Google, and I can't help wondering if this is just a test case or a real use case for them.
Ian has been part of the binutils and GCC communities for many years, and he writes about them regularly on his blog. While developing gold, he wrote a 20 part series of posts about linking in general, and linking ELF for x86 in particular. And if you find that kind of thing interesting, there's Tom Tromey's blog too.