I very rarely pre-order unless there's a pre-order bonus I want to take advantage of, or there's a pre-order discount (such as 800 Reward Zone Points from Best Buy, which is essentially $10.00 in-store credit), but I do plan on pre-ordering the Mass Effect 3 Collector's Edition soon.
Why? Well, assuming it's anything like the Collector's Editions seen in the franchise thus far, it truly will be limited and the odds of getting it on launch day will be next to nil. Better safe than sorry I say!
Update: Just pre-ordered it now. If you pre-order it online at Best Buy.ca here, you'll have $5.00 reduced from the purchase price, which ain't half bad.