Although this one might seem obvious, I've come into quite a few shops lately that don't have the latest service packs.
No software goes out the door flawless - regardless of what a vendor tells you! Microsoft comes out with three or four kinds of software upgrades to the product:
You can find what you have installed by opening SQL Server Management Studio (SSMS) and right-clicking the Instance name. From there pick "Properties" and you'll see the version, edition and service pack listed. You can also run these commands in a query:
Of course, you shouldn't just install things blindly. You need to read (carefully) the "Release Notes" that you find on the download page for the hotfix, service pack or CU, and test the upgrade thoroughly with your software applications.
You can find the latest patches here: http://technet.microsoft.com/en-us/sqlserver/bb671408.aspx
One more thing: if you are not installing a service pack because "my application vendor told me not to", that's bad. If they haven't certified their product on the latest bits, find out why. Be a pest. Most vendors have no desire to do extra work, but it's your system Microsoft is trying to protect, and your vendor won't be the one on the hook when it all goes wrong - you will. Pester the vendor to give you a date and have them tell you what they are doing to certify their product.
I confess that I haven't read readmes or tested updates for at least 5 years. Over time Microsoft updates seem to have become more stable. I would'nt necessarily recommend my approach for everyone but I use a wait a while to install and keep up with the community approach. So I typically wait a month to see if problems surface with a hotfix, longer with an sp and if nothing surfaces on SQL Server forums I just install.
I have had only had one significant patch problem. It occured after installing a set of patches for Windows 2003 servers that hosted SQL Servers. The fix slowed down net traffic and we finally discovered we needed to update our NIC drivers.
Other than that my update problems have been SAN software patches from vendors.
Very good post, I found a list of SQL best practices that might help www.techhelpcentre.com/showthread.php.
I found it useful.