I would also bet on the backlight. Cheapest place I know to get it fixed is http://store.nexttronics.com/replcdblrep.html but so far nobody on the forum has reported having it done there that I know of.
Don't know how the electronics of the inverter/backlight work so cannot explain why but it is one of the symptoms of bad backlight. Dell does not sell backlights. It is an extremely delicate process to remove and replace backlight if you can find one and best left to professionals.
I sympathize with your backlight problem.
I have a two year old Inspiron 600m with exactly the same problem.
I have sent this unit in to Dell for warranty repair but to our dismay the problem was never fixed.
Our problem is a little more intermittent. Sometimes we won't have a problem for weeks on end, but then all of a sudden it happens. Its so annoying I want to trash the whole unit. During the time our unit was in for repair we used our back-up laptop so when we received the Inspirion we gave it a quick check out and it appeared to be ok. We continued using both laptops but alas the exact same problem reared its ugly head in the Inspirion but by then our unit was out of warranty.
Its interesting though when it does happen I put the computer into the suspend mode then put it back into the normal operating mode and the backlight comes back on (sometimes for a minute, other times til the end of my session of an hour or so).
I've turned off screen savers, power savers, etc. and all the related commands to no avail.
I personally think that Dell has an operating system flaw and they don't know how to address it, otherwise they would have fixed our problem when we sent it in under warranty.
Based on funtoupgrades suggestion I contacted Nexttronics in Austin, TX. They think the backlight needs to be replaced. Their price is $149 (don't know if this includes shipping back to me). Their website says they use new backlights, not ones taken from old computers.
I am planning to mail the laptop to Nexttronics. EJN63, what do you mean by "competent LCD shop"? Are these places listed in the local yellow pages? Or are they mail order repair shops? Do you have a recommendation on who is good/bad? Thanks.