A "lag detector" is not the most ideal script in the world. Not only is is fairly pointless (from the stand point of you should be chatting when you have your client on, and can tell what your lag is by doing so), but is also an extreme strain on the server. Think of the 100's of thousands of people on a server, all with a ping script. Individualaly, it's only, what, something like 100bytes. Now multiply that by each user. Now again, by every 30 seconds, 45 seconds, minute, or even every 5 minutes.
Look at a simple 500 person server:
100bytes -> 1 ping
* 500 users -> 50,000bytes (= 48.82Kb)
* once per minute (for an hour) -> 2929.68Kb (= 2.86Mb)
* 24 for one day -> 68.66Mb
* 30 days (avg month) -> 2059.93Mb (= 2.01Gb)
That's 2 gigs of bandwidth a month just because someone wants to have a neat little statistic built into their client. Personally, if you want your ping time, get it as needed. Could be a popup, an alias, or whatever. You don't need to make a nice gui bar graph or line graph or even progress bar just because you want to leave your mIRC running while you play a game or go out for dinner.