Here is my input to this interesting thread.... including the reason why I changed / upgraded.
I am glad that my 'new gear acquisition syndrome' isn't as severe as some others ;D
Camera bodies
1979 - 1995 Yashica film camera - when my parents let me use theirs

1995 - 1999 Olympus film camera - (I gave it away in about 2004 after not using it since 1999)
1999 - 2000 Kodak digital P&S (an early digital camera - used at work, occasionally took home)
2000 - 2001 Fuji F40i P&S (I gave it to friends who wanted a compact digital P&S, I wanted something with optical zoom)
2001 - 2003 Fuji 6800 P&S (zoom mechanism failed - but many photos in the meantime)
2003 - 2005 Fuji F60z P&S (a child broke it - but many photos in the meantime)
2005 - present Canon 350D (works flawlessly. About 100k photos. Weaknesses: AF, low light, poor handling)
2009 - present Canon 7D (a great handling camera producing high quality images).
DSLR lenses & major accessories
2005 - present Canon 18-55mm (kit) (basic, but still useful as a very light travel kit)
2005 - 2011 Canon 28-135mm USM IS (have just sold this. Good lens, but superceded by 15-85mm)
2005 - present Canon 50mm f1.8 (can produce great images, but buggy AF so annoying @ f1.8 )
2005 - 2009 - Lowepro 150 AW (given to friends who were going overseas on mission work)
2006 - present Canon 100-300mm USM (decent build quality, image quality decent stopped down @ 300mm. Will sell it)
2007 - present Sigma 10-20mm EX HSM (great quality ultra wide zoom!)
2008 - present Lowepro Slingshot 300 (useful for taking lots of gear on walks)
2009 - present Lowepro 170 AW (my 'daily travel' bag - can hold my 7D & any 2 of my lenses)
2009 - present Canon 100mm f2.8 USM macro (fantastic macro & also useful for portrait)
2009 - present Hahnl remote shutter / interval meter (fantastic for remote release & time lapse photos)
2010 - present Canon 15-85mm USM IS (my most used 'go to lens'. Very sharp, contrasty, super useful focal length & IS)
2010 - present Manfrotto Tripod & head (really a must for macro photography and benefits many landscapes)
2010 - present Canon 70-300mm L USM IS (my highest quality lens. Super sharp, contrasty - even wide open @ any focal length. Still a travel comfortably size / weight!)
2011 - present Nissin Di866MkII flash (to enhance my exploration of the world of flash photography)
Paul