Initial thoughts:
600D: There seems to be very minor improvements from 550D. the sensor, metering system are exactly same. Canon has instead concentrated on the weakness of the rebel series, ie the grip. Initial impressions at DPreview suggests that the grip of 600D and 1100D has improved considerably. In addition 600D now enjoys wireless flash capabilities. Oh and of-course articulated screen. The price is USD 900 with kit lens (which are also new, but no difference optically).
1100D: This seems like a good upgrade from 1000D. It has got 9 AF points (6 Cross type) from 7 in 1000D, I feel this is the best improvement, I am seriously handicapped by the AF points on a 1000D. A 12mp sensor from 450D. A 63 zone metering mode (again a major improvement from 1000D). A better battery (700 shots compared to 500 shots of 1000D). And a better grip, a major gripe according to critics earlier. At USD 600 this makes a very good entry level camera now..
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Oh and ofcourse 1100D now has 720p video recording...