Since it's launch into the mainstream in the 1990's ADSL has become a very cost effective ways for small businesses to perform large amounts of Internet activity without having to pay for expensive corporate level T1 connections.  However as with most things in life "you get what you pay for".  The fundamental problem with low cost ADSL connections is the service level agreement.  We get many calls to our support desk with reports of ADSL downtime, most of which are for brief periods however we have had cases of ADSL connections that have been ‘down' for up to three days.  Because of the organic growth of ADSL the technology  the telephone exchanges are under constant pressure to cope with the sheer demand and resolution of common problems can become a lengthy process.  Some ISPs (Internet Service Providers) are starting to offer response or fix times with meagre compensation but that's of no reassurance to a small business that has been left without email or Internet connectivity for a number of days. 

One low cost workaround is to install a secondary and lower specification ADSL connection (perhaps through an alternative provider to the primary connection) that remains dormant until it is required for failover purposes through an inexpensive router.  If you have your own mail server the mail records could be pointed to both connections so the process is seamless, surprisingly failover has had a very slow uptake.  I'm sure the investment of around £500 a year must be worth a more than business losses through potential email and Internet failure but as they say "you get what you pay for".