Very good to see more sites utilizing the GitHub API. I do have a few comments to make though. First, you mention badges on the homepage, but this feature isn't complete so I don't think its even necessary to mention it yet. Second, the search is somewhat confusing. I'd love just a single search box at the top of the site where I can type whatever I'd like. Maybe make the current search the "Advanced Search". Third, I probably wouldn't emphasize the tagging so much. I'd probably never tag anything and rely entirely on the data you're gathering from GitHub. I think it's much better to focus on the sorting algorithm and how easy it is to find popular repos.
IMHO it's a bad thing. Too many projects and services depend on github so that downtime represents a systemic risk (homebrew was unusable during the downtime last week). Sure, you have your code backed up, but you don't necessarily have your issue tracker or gists backed up.
Now using GitHub for user credentials makes things even worse. Soon we'll see horror stories involving github being down ...
We encourage all GitHub apps to use proper caching on their end. There's no good reason that a hit on a 3rd party site like Gitrep should relate to one or more GitHub API calls. Use HTTP conditional GETs to retrieve data, and any 304's (cache hits) will not impact your rate limit.
Based on its support of tags/searching, I'd imagine Gitrep is being responsible here though.
You can say the same for Twitter, Facebook and Google. There is always the potential for downtime, but users generally don't want to create more accounts. I think the advantages outweigh the disadvantages. Plus, sites that use GitHub logins are much more appealing to developers rather than sites that use Facebook or Twitter logins.
