Interesting statistics just came out on AlertSite blog post about performance and response time of various highly trafficked social networks.
Unsurprisingly, Facebook is the fastest, and Twitter is the slowest. Facebook has so much more data to deal with, so much media, and so many more users, that it really is a shame for Twitter with it's 140 character data set to be in this unglorious last place.
After continuous reports about migrating to Cassandra, Twitter still serves their tweets out of MemCaches that sit in front of MySQL. When those caches die, it takes a long time to refill them and the site yet again drops the very familiar Fail Whale.
Perhaps Twitter's infrastructure group could use some new blood to work on scaling and up-time. I am guessing that adding experienced people who scaled Facebook, or other high traffic sites could really help in the long run. The problem is that hiring experienced contributors to work on this pain point may feel threatening to the existing crew who continually tried and ultimately failed to fix Twitter's performance problems. Don't fall into this trap Twitter: people who are having hard time re-engineering current architecture will continue to have a hard time without an influx of fresh energy and new ideas. Consider making the necessary changes, and then perhaps you could pull out of that miserly last place.