Donny,
Since you're a "PC" guy, I'll anticipate some of your other questions. Hopefully some of the following will be helpful for you.
() No. There is no common file system that you can view and access. iOS keeps all files on the iPad in "walled gardens" associated with specific apps. Thus, you cannot access a given file from separate apps. Each app will maintain its individual copy of the data object (file.) For the most part this is not a deal breaker (and can be overcome if you jailbreak your iOS device but that is not currently possible with iOS 5) but it can be confusing and annoying (to say the least) if you're accustomed to accessing, say, a PDF file with different applications on your PC.
() Yes, there are ways to edit MS Office documents on the iPad. You have a choice between the native Apple apps in iWorks (Pages, Numbers, Keynote) and various MS Office "emulators" (Documents To Go, Quick Office HD, etc.) None of these solutions is perfect and each can fail with complex MS Office documents (be especially careful with spreadsheets).
() No, there is no way to create separate "accounts" on your iPad as you can on a PC. The iPad is considered to be a very "personal" device. So if you want to share your iPad with others (e.g. your spouse, your child) you'll have to use some imagination and agreed upon procedures to prevent "stepping on one another."
() Sharing your contacts, calendars, and email between your Windows laptop/desktop and the iPad is a complicated topic. Some issues are easily solved. Others are extremely difficult to solve. Proceed carefully if you have a complicated set of requirements.
BTW, I'm also a "PC guy." And despite some frustrations, I find the iPad to be a very valuable device and (with some limitations) relatively easy to integrate with a PC. It doesn't replace my (multiple) PC's but it fills a valuable niche in my configurations.