That's exactly what I did. I'm a senior in high school with 2 classes (hours) of school a day. So from about 1pm to 12am, other than pausing for dinner (When I leave the GECK/CK open) I'm using it. So I maxed out easily at 15 hours in one session with the GECK, and so far have pulled a 4 hour session in the CK. I've never experienced this issue or my mods become 'useless'...
Well, following your post, I looked online and couldn't find any proof of the corruption statement, so I guess I'll take your word for it. Maybe it's a problem specific to Giskard. Or maybe it just doesn't exist, and he confused it with something else.
Well, I'd suggest not taking too much of what the guy says as truth without independent confirmation. Yes, he's right about the navmesh bug, but there's a whole lot of rambly nonsense he's NOT right about.
Yes, the CK can corrupt your mod. It's happened to me twice, but neither time did it have anything to do with actually leaving it open for long periods of time while I was working on it on and off. I didn't do but one mod for Fallout 3, and it never corrupted. Even with as unstable and broken as the Oblivion CS was, it never corrupted a mod I worked on unless it crashed in the act of saving.
The Oblivion Construction Set is
FAR from unstable and broken. In all my time playing around with it, I've encountered very little mod-breaking bugs. The only time I've ever lost a mod is when the computer completely blacked out in the middle of a save (complete black screen, looping sound, completely unresponsive until I shut off the system. Only ever seems to happen when I use the CS for a long period of time. It's happened before.). And that's probably a problem specific to my computer.
True, the Oblivion CS is not infallible. It has its share of buggy features (the Heightmap Editor, for instance.), but nothing that can't be worked around, or can stop you from getting on with your work.