From conversations with clients, it would appear that a lot of people are unaware that Exchange 2010 Service Pack 1 is no longer supported.
I am still seeing clients who haven't upgraded. These range from SBS users right up to multi site Enterprise clients.
The Microsoft support policy on service packs is that when a new service pack is released, the previous service pack only is supported for a further 12 months.
The support of Exchange 2010 SP1 ended in January 2013, Service Pack 2 ends in April of 2014.
If you are still on the original release, known as RTM, then support ended in November of 2011.
This shouldn't be confused with support of the product Exchange 2010, which will be supported (as long as it is on the latest service pack) until 2015, with extended support until 2020.
The full table for support can be seen here:
If you are curious about Exchange 2007, then those dates can be seen here: