No - you can leave it in.
People who think it should be removed, or people who advise it are usually thinking about the "Memory Effect". NiCd (Nickel-cadmium) batteries were affected by this, however new Li-ion (Lithium-ion) are not affected.
On some laptops, (especially "green" laptops with specialised power chips) you will get poor performance with the battery removed as it under-performs. For example MacBook Performance Plunges When Battery Removed.
Any intelligent laptop from the past few years should be intelligent to discharge and rotate frequently meaning that you do not need to manually drain it. For example, my laptop is plugged in (usually) 24x7, and every 24-48 or so hours, it drops to 95% and recharges.
Lastly, One bonus of having a laptop is that you get a "free" UPS! of course, if you have a separate UPS, forget this point, but if there is a power cut, you may be happy that you left it in.
Like you'll still be using it after two years, when this effect actually gets noticeable... – Ivo Flipse – 2010-01-06T07:57:00.467
Possible duplicate, or some relevant thoughts http://superuser.com/questions/92011/should-i-remove-my-laptop-battery/questions/12358/is-it-better-to-use-laptop-on-battery-or-on-ac-power
– outsideblasts – 2010-01-06T08:05:03.553Thank link from @outsideblasts should be: http://superuser.com/questions/12358/is-it-better-to-use-laptop-on-battery-or-on-ac-power
– Svish – 2010-01-06T08:36:14.053Thanks, Svish. Don't know what happened to my pasting there. – outsideblasts – 2010-01-06T09:06:48.437