Much desired new feature - should make the CRUD procedures a bit easier
I like the idea floated about flagging records as deleted rather than actually deleting them. I haven't experimented with 2008 yet (and a few of our customers are still running 2000 so I cannot even take advantage of this for a while!) but I think there will be many creative uses for the command as you needn't necessarily insert a record when not matched, just as you needn't necessarily delete.
Presumably only a single command can be executed - no begin/end blocks? Also, I would assume that the command has to be set based rather than, for example, a stored procedure execution (which would make the command cursor-based and ugly).
I would think the merge command allows the query optimiser to have some smarts such as avoiding multiple table/index scans that may occur if you do the
IF EXISTS... UPDATE... ELSE INSERT... (although the optimiser may already recognise this - I haven't checked lately).