Before you ask the question "at what point does outsourcing make sense", I think you have to look to see what your organic assets are, and what your IT department?s core competencies are.
Example: If you as a business owner want to bring in a new ERP, Supply Chain, CRM software like SAP on board I bet you don't have organic SAP experts within your IT staff. At that point, you outsource what you need, because you probably could not afford a whole staff of SAP experts that were permanent employees.
Another thing to ask yourself is what you can outsource that will free up your IT staffs time to work on other more important projects...
An area that companies completely overlook is finding a hardware vendor that can also take over the Imaging of your PC's (Get standards in place), to make the PC's plug and play. The extra $25 for the PC to be imaged is probably less than the time it will take away from your IT staff for those projects they are late on. Have your vendor assemble and test your servers, install windows server, and even your application, and the patches you want. Time is money, how much time does your staff waste on menial tasks??
My point is to use outsourcing to streamline your IT departments, and avoid wasted time.
If a job is just time intensive and not very skill based, out-source IT.
Got a large PC rollout? Need Extra Bodies to put PC's and new monitors on a desk, and put the old one on a pallet for disposal? Outsource... Think of outsourcing as TEMPORARY LABOR...
If a temp is what is needed, Outsource...
Need a programmer for 90 days to 6 months? Outsource... Yes he will cost a little more an hour than a full time employee, but if you only need him for 6 months, the cost of benefits, training, and other hidden costs will quickly eat up the savings you thought you were going to get (what are you going to do, hire and fire people ever few months?)... Plus if you need the same programmer a year later for 90 days more, via outsourcing, he'll be happy to work for you again... If you hired him and fired him after 6-months he'll probably tell you to take a hike...
All companies outsource something? Don?t believe me? Who provides your electricity, water, sewer service, telephone service, Air Conditioning & Heating service, etc?? Unless you are an electrical company I bet you don?t have organic electricians?