Apply SQLServer Service Pack to a Single Node Cluster I have to apply a SQL Server 2008 R2 Service Pack to a Single Node Cluster. 

The other node died and new hardware has been ordered. 

Is there anything weird to worry about?

Normally we'd apply the service pack to the passive node first, then failover, and apply the service pack to the newly passive node, however this clust only has 1 node. We're loading Service Pack 2 so we can upgrade to SQL Server 2014.
Nothing particular to worry about, but you will incur downtime as the SP runs its stuff in "script mode" during which users cannot connect.

It might go without saying, but I'd ensure you have a valid (i.e. tested) backup of the databases (including the system databases) on the affected system prior to doing any patching, whether on a single-node cluster, a multi-node cluster, or even a stand-alone instance.  You can never have too many backups.