Digg, Twitter, Facebook Connect, OpenCalais and what not can be configured to submit a new node or comment upon submission. This works for small sites with low volumes, but even then it slows down the form submission: you have to wait for the third party server to process your request and send back an "OK". If the remote servers are slow or down, it may even cause a local "traffic jam" in your system. Apache processes will hang until the remote server replies.
If you really don't need such web 2.0 modules, then don't use them. At least not directly on node or comment submits. The right approach is to build a custom module that fires on cron runs to submit such request, e.g. once per hour.
- Avoid hanging Apache processes
- Reduce time it takes to submit a node or comment form