I've had my 36ZT29 since the middle of August. It's been in constant use but the dark sides are as strong as ever!
If it weren't for this problem this would be a brilliant set. Mine has near perfect geometry and has none of the other faults reported in this forum.
It's a real shame that this otherwise superior TV has to be let down by a shoddy tube. As a result I'm swapping mine for the Sony KP44PX2 rear projection set. There doesn't appear to be a 36" crt that doesn't have problems so I've ruled them out all together.
What's the point in having all these picture enhancements such as Progressive Scan, if the the whole viewing experience is overshadowed by dirty marks down either side of the screen? Toshiba need to get their act together!