I've noticed the Twitter API is very slow and unreliable. Requests often take 10+ seconds to return. Sometimes they timeout with no response at all.
I put together some monitoring tools to see exactly how slow and unreliable the API really is (when it is even available!). This is obviously not a very scientific test; just a ballpark idea of performance. The monitoring tools are built with Python and RRDTool. To start with, I used a modified version of my rrdpy suite of tools (http://code.google.com/p/rrdpy).
I ran a test for 2 hours, hitting the API's Test Method every 30 seconds. The tools generated the following time-series graph of server response times:
The average response was 2.53 seconds, and we see a *lot* of variance in the data samples.
In comparison, here is the same test run against the Yahoo Search REST API:
Notice the small variance and the average server response time of 0.186 secs!
I would be interested in running these tests again in a few months to see if Twitter's API has become faster and more reliable.