I've done four tests in total, the last one was on Friday.
First test was two days after my period was due, and was quite faint (took it mid afternoon), the second test I took the next day first thing in the morning, and it was roughly the same. I took another test 3-4 days later, and it was as dark as the control line, which reassured me a little.
The one on friday was because I wanted to use a clear blue conception indicator thing - it said I was 2-3 weeks (since conception) and that was the day before I hit three weeks since conception. It was just reassuring to see I was approximately on target for where I should be.
Looking - I'm not sure what you mean about the pregnancy test staying positive until you next ovulate. It doesn't have anything to do with ovulation, it's the level of HCG hormone. So, if you taken a test and it was a very strong line, then you take the same test again a week later and it's a very faint line, then it would indicate that your hormones were dropping, which isn't a good sign.
I always thought people who took lots of tests were mad, but I can totally understand it now. It's basically the only thing to prove to yourself that you are actually pregnant!