I haven't "switched" and I wouldn't recommend a switch. An iPad or other tablet is a great supplement to a real computer, not a substitute - unless what you do is mostly in the "cloud," and I don't know anyone who's actually there yet (other than with fitness stuff). (The keyboard is also basically useless, so you would want an add-on physical keyboard - there are several choices. If the iPad 3 gets the haptics right, that may eliminate that issue, but that's some time in 2012.)

How old is your desktop? Almost nobody needs a desktop computer these days. If it's newer, you might consider a netbook to replace your laptop; if it's older, I'd get the zippiest laptop you can afford to replace them both.