What do you guys think?

I have always been a firm believer in warming up my engines before I start my daily driving. My normal routine is to start my car 5 minutes be for I depart in the summer and 15 minutes in the winter. I have been doing this for many years now and my engines have shown no internal wear.

I since have heard from a couple sources that warming up an engine too much can be bad.... I would like to get opinions on this issue from members here before I permanently stick to my temp cycling regiment.
Thanks!
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320