At some point, I may add an option to toggle off tags, if there is enough demand for it. However, I’m trying to keep the plugin as simple as possible and avoid adding extra options. Here are some possible solutions, barring adding this as a feature;
First, the user will have the option to edit the tweet as they see fit before posting it. Many quotes will be too long to tweet even without tags, so this gives the person sharing the quote more control over what they share. In other words, it’s not necessarily a bad thing if a tweet ends up being too long initially.
To build on that logic, I had at one point considered limiting the length of the tweet text to a certain number of characters. Less than 140 for example. I decided not to hard code that into the plugin, but if you would like, you can enforce a tweet length by adding the following code on line 134 of quotable.php;
$tweettext = (strlen($tweettext) > 140) ? substr($tweettext,0,120).'...' : $tweettext;
That would cut any text longer than 140 characters down to 120.
Finally, another thing you might consider (which, understandably might not fit into your content strategy) is to use less tags on the post, but that shouldn’t be necessary.
As far as the url short link, Twitter will automatically shorten longer links, so that should be a non-issue.