Well, going back to what I was saying, the t3i doesn't have a PC sync, so you'll need to get a hot shoe adapter. This isn't a huge deal, but it is a pain. My a350 didn't have a PC sync, and I kept misplacing the adapter. It's not a huge deal, but it is a nuisance.
These entry level cameras typically have lousy viewfinders. The t3i is no different, it's small (0.87x) and with a short eyepoint of 19mm - so if you wear glases, this will be pretty annoying. It's a pentamirror, so it's going to be dimmer than a pentaprism.
The build is likely going to be pretty plastic, and with only one knob you'll have to press a button to adjust both shutter and aperture, or EC value. Without much experience, this might not seem like a big deal - but as you use exposure compensation more, or opt to shoot in manual mode, it will.
You're not going to have any weather proofing at all. This means that if it starts raining, you run a real risk of substantial damage to your camera. Even if you don't get weather sealed lenses, the t3i will let water in around all it's buttons, in the screen, everywhere. Photographing outdoors in the spring will go from "quick protect the gear" to "I hope my camera isn't dead".
Can this camera take good photos. Very much so. But it's not the image quality so much that is what makes it less than "professional".
A better alternative at a similar price is the 50D or D300.