A first generation product is rarely without flaws. While it may represent the most bleeding edge of a new technology, it often comes at the price of having several rough edges that are usually smoothed out in future iterations of that product.
While it may be too early to say for sure what the flaws are with the new iPad (aside from the omissions of certain features such as a webcam), early reports are pointing to problems with the Wi-Fi and potential sensitivity to heat.
Users of the iPad are reporting that the wireless signal reported by the tablet is weaker or less reliable than other products in the same vicinity. Several stories from the web, including those from TUAW, AppleInsider, and TechCrunch mention personal experience and other forum posts detailing Wi-Fi woes. One theory is that the aluminum back casing is blocking too much of the signal, or that it's a software issue.
Another problem cropped up through use from the masses is reports of overheating, forcing the iPad to lock up with a temperature warning. As mentioned in stories from MacNN and CNet, users from California, Texas and New York report that the iPad got warm enough that the screen displayed a warning icon along with the message, "iPad needs to cool down before you can use it."
One user put his iPad in the fridge for a short while to return the tablet back to the mood needed for operation. While we're not yet sure of what temperatures the iPads were used but, Apple lists operating temperatures of the iPad at 32° to 95° F (0° to 35° C), which could easily be exceeded if exposed to sunlight for a length of time.