Hi, just joined the iPad Forums. I pre-ordered my iPad early enough to get it the day before they went on sale in the UK stores, so I've been playing with mine for a week so far.
First impressions: Fabulous user interface, a good selection of iPad apps (rather than just iPhone apps expanded), battery life is good (more than a day's use).
The biggest negative is the lack of file management - not being able to access files independently from the applications that create them. So, for example, if you want to send an email with an attachment you have to go into the app that you used to create the attachment and email from there. There are a couple of apps that help a bit (e.g. GoAruna, GoodReader) but the problem is still there.
I got the cheapest device (WiFi only, 16Gb) and I'm beginning to regret not spending the extra £100 to get the 3G version. But I've just bought a Zoom mobile wireless router and a pay-as-you-go 3G dongle from Vodafone, so I should be able to carry my own WiFi cloud around with me wherever I go (as long as I have 3G access). I'm planning to start trying this out later this week.
Interested to hear any tips from other iPadders