Blog feed not updating consistently

This is related to the time stamps on the items. Looking at your feed, as I am writing this the most recent item posted to twitter is "Show off your vintage style...". This item has a time stamp (the "updated" attribute) of "2008-07-09T18:51:12Z".
There are more recent entries (for example "get crafty..."), but their "updated" time stamp is actually older - "2008-07-09T08:00:43Z", so twitterfeed doesn't post them because it checks every item against the timestamp of previous items. So once you have an item in the feed that has an "updated" value that's later than the one in the above "vintage" post, twitterfeed will post it.

If you wanted to try and get around this, you could try setting the "post new items based on GUID" option in the twitterfeed settings, since this will ignore timestamps and just look at the items' GUID.