Do you live close to an Apple store? Many of the big malls have Apple stores, and the kids who work in those stores can answer all your questions. You can also call Apple 1-800-myApple and they will help you with your concerns. It is true that there are some programs designed for the PC that will not run on the mac. If that is a program the you must have, then that will be a problem for you.
Oh yeah, if you ever do have a problem with your Mac (rarely), you can take it to the Apple store, and the kids there can usually fix it.
You don't have to worry about upgrades, whenever there is an upgrade for your operating system or to any standard Mac program (e.g., iPhoto or iMovie), you get it automatically. You have a program on the Mac that checks weekly for upgrades for all your systems and programs and you get a dialog box asking if you want to upgrade now, you say yes, and agree to terms and then the mac installs the upgrade.
Of course, if mac develops a whole new operating system, then that type of upgrade wouldn't be automatic. It's my opinion though, that mac operating systems are so great, it wouldn't matter - you could easily wait till you were ready to get a new computer.
I know it sounds like we are trying to "talk" you into a mac - the truth is though, that we love ours so much, we want you to take a look at Macs. But if it is not right for you, then don't be swayed by our enthusiasm!
Good luck!