Many businesses in the US still use T1s for their data connection, even though it is an out-of-date technology. T1s are based on early generation SONET fiber which was designed to carry large numbers of phone calls in the core of a telco network. In these networks, the bandwidth is divided into 'containers' that are well-suited for phone calls but are irrelevant to the Internet and data that most of them are used for now. These containers are traditionally a fixed size and inflexible, and depending on the mix of data and voice traffic that must be carried, can be very inefficient. The advantage of a T1 is that it comes with a promise of the 99.99% 'four nines' reliability that you expect of the telephone network, which translates to less than an hour of downtime per year. The disadvantage is that you are paying a significant amount per Mbyte for the bandwidth.
As with any access technology, your options depend on your location. In urban areas, you probably have a choice of fiber to the premises—both business and consumer versions—Ethernet over copper (EoC), cable modems and DSL all of which will be much more cost effective than a T1. You are likely to get a 10Mbit/s EoC connection or even 50Mbit/s fiber for less than the 1.5Mbit/s of a T1. If you are in a rural area, T1s may be as good as it gets but it's worth checking whether high-speed wireless is available since it's likely to deliver higher speeds at a fraction of the price.
In general, business services come with better performance guarantees known as Service Level Agreements (SLA's). For example, business service SLA's guarantee symmetrical bandwidth for both upstream and downstream traffic. If your use is mostly email and web access, then a consumer grade fiber or cable service is fine. If you are running servers on your premises that need to be accessed remotely, or if you are using a VoIP phone system, you need to be sure you have enough upstream capacity—the bandwidth quoted in consumer ads is likely to be for downstream only. The key takeaway is that when your business is in the market for more bandwidth, do some investigation and don't just add another T1 or upgrade to DS3 without checking out the options available in your area.