I pulled out a WRT54G the other day and set it to a 56K limit. A netbook running ubuntu(ish) took several days to complete an apt-get update. But when I connected my laptop with 50 browser tabs, the tabs themselves consumed 100% of the bandwidth with background traffic (despite my ad blocker) and no other network services worked at all.
Unless you've tuned your system for it, dial-up modem speeds are functionally equivalent to "no connection at all".
Timeouts are killer too... many modern apps assume slow or no response for more than 10 or 20 seconds is "Internet is down" and will stop trying.
It's brutal, even with modern Internet, when people develop apps with the assumption of the Internet connection always having decent latency and bandwidth.
Unless you've tuned your system for it, dial-up modem speeds are functionally equivalent to "no connection at all".