RIM BlackBerry PlayBook demoResearch in Motion’s BlackBerry PlayBook tablet will hit store shelves on April 10, multiple sources tell the mobile site Boy Genius Report.

That date falls in line with RIM’s plan to release the tablet some time in the first quarter. BGR says that the OS will be finalized on March 31, but users will be prompted to install an update as soon as they boot up the device.

I expect we’ll hear even more leaked information on the PlayBook soon, as it would be a good way for RIM to subvert the iPad insanity brought on by today’s iPad 2 launch event.

Also in PlayBook news, HP apparently isn’t taking too kindly to the tablet’s slick multitasking interface. Jon Oakes, HP’s director of product marketing for the WebOS-powered TouchPad tablet, apparently considers the PlayBook’s interface a WebOS imitator.

Speaking to Laptop Mag, Oakes said:

From what we’ve seen in the market, there are some uncanny similarities. It’s a fast innovation cycle and a fast imitation cycle in this market, so we just know that we have the creative engine here to continue to build on what we have, and we’ll keep innovating, we’ll keep honing and those guys hopefully will continue to see the value in it and keep following us by about a year.

RIM, to its credit, responded by saying that the PlayBook’s interface is just the result of good design. RIM senior vice president for business and platform marketing Jeff McDowell likened the situation to how competing cars end up looking similar after going through a wind tunnel. He also said that QNX, the software company that RIM bought last year and whose OS powers the PlayBook, may have had that interface in mind before they started working with RIM — which shifts any blame of design imitation from RIM to QNX.