Research in Motion is now officially in the tablet business, as its Playbook hits stores today in the U.S. and Canada.

The new 7-inch tablet will look to compete in a world dominated by the iPad, whose launch weekend saw massive sales and later saw demand that caused worldwide shortages. People were even scalping them right outside the Apple Store in NYC for ridiculous markups.

The PlayBook is now available to the masses in 16 GB, 32 GB and 64GB models.  These will run you $500, $600 and $700 respectively.  The PlayBook is currently only available with wi-fi, as 3G capability is set for later release.

The PlayBook was announced 7 month ago and the version that is being released today is virtually the same as the original model, both in specs and function.  Reviews have been mixed, with many lamenting the tablet’s lack of a native calender or email client.  The reason for this is that the tablet is supposed to be a companion to your BlackBerry device.  Besides this complaint, many reviewers have enjoyed the look and functionality of the PlayBook.

How are opening day sales?  Reuters reports that they may be lackluster, at best.  They detail less than enthusiastic turnout at two particular locations:

Customers trickled in slowly at stores that opened early, in comparison to the throngs that flocked to stores when the iPad 2 was introduced a month ago.

At a Sears department store in downtown Toronto, just five people showed up for the 7 a.m. opening.

At an Office Depot store in Midtown New York, three PlayBooks left the shelves within 20 minutes of the store opening, while not a soul stirred outside a nearby Staples store.

It is unlikely the PlayBook will be able to initially compete with the iPad.  Apple sold about 15 million original iPads in 2010.  Analysts projects about 3 million PlayBooks will be sold in a similar time frame.  But Blackberry users are loyal, and many may like the idea of tablet-as-companion-device to their much loved phones.

Although the device is making its wide release today, its official kick-off party happened last week in NYC.  Entertainment Tonight’s Nancy O’Dell and NBA superstar Dwight Howard were featured celebrity guests.  Mixed reviews be damned, as Dwight Howard threw his support behind the device on Twitter: