Hi wolfy68,
...if you think the only difference is MP and dust removal, please read and compare again
)
Build and size is another difference, 'plastic' and (still a little too ?) small for 400D versus 'magnesium alloy' and 'mediumsize' for the 30D.
And how fast or how much do you need to shoot? 30D does 5 fps for 30 images, 400D does 3 fps for 27 images.
400D misses spot metering
400D has no ISO HI (ISO3200) capability
Max shutterspeed is 1/4000 for 400D, 1/8000 for 30D
Batterypower: approx 400-500 images w/400D, approx 800-1000 w/30D on one charge
etc...
IMHO the 30D remains the more desireable camera, but they have been getting awfully close...
...so watch out carefully whether you really need the 'added benefits' of the 30D, or like the newer features of the 400D more...
...and if anything: go to a shop that has both, and compare how they feel 'in your own hands'
As for your other question, what classifies a pro, semi pro or amateur camera:
Nothing, really, if a Pro is making his living with a 300D, then that is his 'Pro-camera'. If an amateur uses a 1Ds Mk 2, that is his 'amateur-camera'
Depends on the shooter, NOT on the camera, IMHO
Hope this helps some, *my* little €0.02 worth...
Kindest regards!
Max@Home