What you are sharing, when you have cable internet access, is the segment. You and your neighbors are all part of a Network segment (which makes a broadcast and collision domain), as opposed to DSL which is switched. The difference? Your cable modem will see all traffic on the wire, meaning your neighbors traffic. It must also share the available bandwidth with the other persons on the segment (ie... your neighbors). In a DSL circuit, you only see traffic meant for you (for the most part, few exceptions) and you are on your own segment (your own collision domain, own broadcast domain in most instances).
So true, your "geeks" at work are correct. But that depends on if and when your neighbors decide to get broadband, and then select cable as the way of access.
But if I were you I would just benchmark your speed test results and monitor it now and then to make sure you are not losing too much to the sharing nature of a cable internet solution.
Some places to test your speed (use more than one, as several factors can give you inaccurate results):
Bandwidth Place
DSL Reports
CNet
MSN