I've found an offer for T4i or T3i at the same price. Is there any strong reason I should stick with T3i and not upgrade to T4i? I'm asking this because of the obvious success of T3i, which is sort-of intimidating me to go for the upgrade.
You should almost certainly go for the T4i if the price is the same or similar. The T4i has better technical specs and features, including video auto focus, cross-type focus points and faster continuous shooting. The T4i is also thinner than the T3i.
Snapsort provides good analysis of cameras from their specs and also compares cameras face to face, contrasting their good and bad points.