I reckon in 8-18 months, cannon would release AKA 600D and 550D will prolly be degraded and becomes obselete.
* Why dun u save some dough and go for Canon EOS7D (Semi Pro And Mag Alloy WITH FULL HD)
Why don't everyone invest in something that will never go obsolete? Get better in your skills. Read, learn, try more. Get better.
In the end, whether you are holding the newest camera, or 1 to 2 generations behind, if your skills suck eggs, you still end up with sucky pictures.