When upgrading to os x lion, will all my files stay in place or what?

Question

when upgrading to os x lion, will all my files stay in place or what?

Answer 1

Yes of course, Apple knows a users files are valuable and won't just go deleting them .
However, OS X upgrades can go bad due to unforeseen circumstances or special modifications people have done to their operating systems or even root level anti-virus installs like Norton.
If the upgrade goes bad, your operating system can become "bricked", requiring a lot more effort to recover your files.
Also third party programs like from Microsoft, Adobe and others may not be ready for OS X Lion, if you have any "mission critical" needs for the computer, it's best to wait several months, yes SEVERAL MONTHS, to make absolutely sure all the bugs are worked out of third party drivers, software, printers, scanners etc., and even OS X Lion itself.
Always backup your valuable data, to write protected cd/dvd's if all possible for the reason that humans, even myself I just recently learned, can very very easily erase data on re-writable media like hard drives due to human error.
TimeMachine is a somewhat ok image backup system, Carbon Copy Cloning of one's boot drive onto a external drive which is hold option bootable is great in case your hard drive dies, but for your most precious data, you really should be burning, labeling, dating and storing multiple cd/dvd's.