What type of tablet do you want?
The iPad has burned the image of the modern tablet into everyone's brain. Small, thin, with a display size of about ten inches, the iPad is certainly sexy and it's great for games and media.
That's not the only way to build a tablet, however. If you choose to go with a Windows 7 tablet PC you'll have a two different formats to choose from. Many products do have the slate form-factor of the iPad, but the make their own modifications. The ASUS Eee Slate EP121, for example, boasts a giant 12.1" display.
The other format - the one you don't often find elsewhere - is the convertible. A convertible tablet is a full laptop computer with a screen mounted on a swivel hinge. You can use the product like any other laptop, then swivel the display around and use it as a Windows 7 tablet PC. This is a popular choice for people who want a tablet for productivity reasons; for example, digital artists sometimes use this sort of device for their work as it allows them to use a stylus without lugging a drawing tablet around.
Generally speaking, Windows 7 tablet PCs are best for people who want either a convertible or a very large traditional tablet. While some Android convertible tablets are close to market, they're unlikely to provide an experience on par with a Windows 7 convertible tablet in terms of processing power.