As a person who owns a desktop, laptop and 7" Nexus 7 tablet I will tell you that a tablet cannot fully replace a laptop.
The main advantage of the tablet is that it is portable. I use it primarily for reading and studying and the occasional video (study material). I also play a couple of pinball games on it (much easier than on a 4.3" Android phone). I basically use it for "consumption" only purposes. Occasionally I will write an e-mail or surf the next, but I find doing those much easier on a laptop. Of course if you are standing on a street corner it is much easier to do those things with either your cellphone or tablet. Some websites (like THG) detects if you are connecting a phone/tablet or laptop/desktop and routes you to their "mobile webpage" rather than the standard webpage. I find that rather annoying and when you type the on screen keyboard take up almost half your screen.
If you are doing any work, then you will likely find using a tablet to do so can be quite irritating because the keyboard takes up a decent amount of screen real estate. Typing a quick e-mail or text message is generally not a problem, it's when you are doing any actual work that it becomes an issue. I use spreadsheets a lot an the spreadsheets available for tablets are rather weak / lite compared to something like Office 2010 for a laptop.
A tablet makes a nice complement to a laptop for traveling purposes because it is easy to whip out the tablet if you need to quickly reference something or entertain yourself by reading or watching a movie. And it's just as easy to put it away. I keep my Nexus 7 in my inner jacket pocket.
There are Windows 8 tablets, but I never fully researched them. I just know they do not offer an acceptable amount of processing power for me to drop money on them just yet and I am not specifically looking to replace a laptop with such a device.