Google Code was such an improvement over SourceForge. I think the real problem of Google Code was that it took them too long to support git. When GitHub started Google Code was still SVN only and later they only added Mercurial support. This made people look at GitHub and GitHub could shine with some new ideas, like making code contributions extremely easy and placing the code first. Which of course further increased the popularity of git and so on. By the time Google Code added git support many major projects had moved and GitHub was simply the place to be.
" I think the real problem of Google Code was that it took them too long to support git."
Yeah, this is true. Part of it was that it was going to require a ton of work to fit Git's concepts and protocols (remember, git only started supporting smart http in 2010) into the infrastructure we had. It wasn't until the storage backend for code was completely rewritten, and better http support was added to git that it really became feasible.
(Note that Google code has a completely replicated storage backend infrastructure. It's not just a ton of git/mercurial/svn setups)
It's really funny to hear this. If you look at press/reviews/OSS forum comments of it around launch time, people thought it had an excellent interface, because it was being compared to sourceforge.
Then github came, and by comparison, the interface looked like crap.
But you end up with this kind of weird history rewrite where the view becomes "it was always ugly", when it was probably best-around for at least 2 years, maybe more (depends on your view of early github)
"Google Code, by contrast, didn't seem to have a clear purpose other than hosting open-source projects. It was a kind of souped-up SourceForge, rather than a serious GitHub competitor. Google certainly had the resources to improve it, but didn't have the motivation that GitHub did -- and we see the results."
It was in fact, meant to be a better-than-sourceforge alternative, because Google viewed sourceforge as a harmful-to-opensource monoculture, and competition was desperately needed. github is a monoculture, but it doesn't seem, at least right now, to be harmful.
As for "serious github competitor", it was never meant to be that. It predates github by over 2 years :)