Cellular technology is widely used for Internet access, also because most operators are now offering Mbit/s data rates at affordable prices. Many studies analyzed the performance of these networks using analytical or simulation approaches. However, due to lack of data from operational environments, very little is known about the performance of real cellular networks. In this paper, we assess the performance of the 3G network of one of the major European telecom operators, using several recent traffic traces of TCP connections to port 80 and 8080. After presenting performance statistics related to all the network users, we focus on heavy users. To assess their performance and to uncover the related causes, we introduce an investigation approach easily repeatable in the very common situation where only data traces are available, with no other information such as mapping of users to cells, network capacity, or packet payload. Analyzing both “single long-lived connections” and “multiple long-lived connections”, we assess the performance of those users, providing insights on how and why performance can vary significantly over time and among different users.