Stu, and others:
To me, successfully getting into, or out of a slip, depends a lot on knowing and being able to control your boat's characteristics under power in forward or reverse, the space and configuration of the fairway, slip, or face pier you are dealing with, and the impact of wind and current on your boat. Perhaps a recent example would help. I was teaching a couple of inexperienced sailors to get into and out of their very tight slip. The boat (their first!) was a mid-80's 36-ft S-2 that probably displaced 16,000lbs and was beamy. A strongish breeze (>12 kts) was on the beam of their boat that was stern-in. They needed to turn to port to leave the slip and the fairway was only about 40-ft wide. Perfect situation to use a mid-ship spring on the port piling. I set the mid-ship spring around the piling and gave the bitter end to the owner's wife while the owner steered out of the slip. I instructed her to pull on the line as soon as the owner shouted that the stern was clearing the piling. She had a hard time being able to pivot the boat around the piling as the wind took the bow the other way (it always does). If the the owner were alone, he could have tied the bitter end to a port stern cleat, yet I think the owner at the helm would have a hard time both steering, pivoting the boat, and then letting the spring go in order to pull it in quickly as he steered out of the slip. Sure, a sailor with a lot of experience would find a way to do these multiple tasks simultaneously, but you'd have to have a lot of confidence, favorable weather, and gelcoat repair at the ready to do so.
On a boat like mine, which only displaces about 7200 lbs and which I sail alone alot, I tend to use and recommend premeasured lines, that stay on the aft pilings, that have loops tied in the ends. I can pivot the boat out the slip in an unfavorable wind with the windward line, and all I need do is grab one or the other, drop it over a winch and the boat stops in the right place when coming back in.
Another technique that is worth considering is what I call "Going With the Flow." If you find that the boat is being pushed by wind or current the opposite way that you want, let the boat go that way (as long as it is safe). People often get into a jam by trying to correct the boat's direction at this point. Once clear of the slip, either back all the way out of the fairway, or do a "pivot turn" to turn the boat 180-deg in the direction you desire.
Lots of practice, on a calm day, and with crew standing by if needed, is the real solution here. Whatever works, works.