There's plenty of hype leading up to tomorrow's new iPad unveiling. Apple (Nasdaq: AAPL) is expected to introduce the third generation of its revolutionary tablet, and the speculative buzz points to a slick handheld device that offers better graphics and processing power. It may even outdo the iPhone 4S by going 4G.

Gadget buffs and early adopters are going to decide whether they want to buy it or not, but investors may very well be going through the same process as it pertains to Apple's stock itself.

The Wall Street Journal offers up an interesting perspective in its "Ahead of the Tape" column. Spencer Jakab points out that -- outside of the original iPhone -- the average one-week performance for Apple's stock after an iPhone or iPad hits the market is a decline of 3.5%.

Ouch!

Keep in mind that this is when the iOS gadget actually hits retailers. Apple's stock has actually historically risen between the time a new iPhone or iPad is introduced -- as it will tomorrow -- and the time it takes to be widely available. The week leading up to the sale date has actually averaged a 2.9% gain.

The column suggests that speculators hopping on now will be well served to cash out ahead of the actual release. It may seem like sound historical advice, but it's never as easy as that.

Some of the chatter in recent weeks points to a "near immediate" release revealed tomorrow afternoon, so traders may not have a lot of time to ride their wagers.

Investors looking to dump their stock (or possibly even short Apple) when the new iPad is available will be flying in the face of a stock that has been a tremendous winner over the past year. Whether or not the stock dips over the course of a few trading days, the smarter bet is that Apple's shares will be even higher when the next iPhone or iPad comes out.

Things may also be different this time. Unlike the first two iPad rollouts, most analysts believe that Apple will continue to sell a scaled-down version of the iPad 2 at a price point that may compete with the entry-level tablets put out by Amazon.com (Nasdaq: AMZN) and Barnes & Noble. Research In Motion (Nasdaq: RIMM) has also tried to move its fledgling PlayBook tablets for as little as $199. Millions of RIM's tablets were sold over the holidays, and it's not a fluke. Pacific Crest analyst Chad Bartley revised his target for Amazon's Kindle Fire higher last month. He now sees the online retailer selling 14.9 million units this year.

There's a chance that tomorrow's Apple announcement may be better -- and with healthier long-term implications -- than past unveilings.

Sellers beware.

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