From Kelly Linden on the scripter's email list:
From: Kelly Linden>
Subject: Re: New Functions and Other News
To: Scripters [email]secondlifescripters@lists.secondlife.com[/email]
... (my edit)
Each mono script gets counted as 64k right now, because they are allowed to
use up to that much. At some point we will allow mono scripts to adjust
(lower or raise) this number so smaller scripts will get counted for closer
to what they use. We strive for some stability and predictability - your
script won't randomly stop working because a list got too big or another
scripts list got too big. Unless you hit the limit you knew about when you
wrote the script.
...
Tools to see how much script resources are getting used are going to come
out quite a while before we start enforcing any limits. This code is in the
simulator already and we will have viewers that allow residents to see that
information out soon.
- Kelly
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So - a few important points there, in case you didn't already know them:
1) Sign-up for the scripter's list if you want to get the latest news

2) Mono scripts are 'always' 64k at the moment, just like LSO ones are 16k (that was news to me - I thought they were already floating)
3) The tools we need to check scripts properly should be out 'soon'