To answer your questions:
1) How are the centerboards raised and lowered? Is it hard to do? Do they all swing down on a pivot or do some slide down (like a daggerboard)?
Most centerboards either have a small winch
that tensions a cable that raises the centerboard. These winches
vary from trailer type cable winches
(electric and manual) to normal sheet winches
in which case there is often a block and tackle on the end of the centerboard penant. The centerboard cable either acts through a tube that is sealed at the bottom and or deck or through a variety of pull rod designs that pass through a packing gland. Centerboards are usually not too hard to operate but drop keels because of their weight take a fair amount of cranking to pull up and down.
Most cruising centerboard boats have pivoting centerboards (just weighted enough to cause them to be heavier than water) or Swing Keels (which pivot and are weighted significantly enought to help act as part of the boat''s ballast.)
There are daggerboard boats out there but those are mostly small boats. There is a current trend in small race boats to have a dagger board with a bulb on the end. These are very efficient sailing wise but are much more difficult to raise and lower and really cannot be partially raised lowered under sail.
2) Are there different designs? What is there to look out for ? What is the maintanence? Will they last the life of the boat? Are they troublesome?
They vary very widely in design, quality and execution from crudely cast iron swing keels, or a rough cut steel plate, to nicely fabricated lead keels, to nicely fabricated fiberglass foils, to crudely fabricated glass over plywood. In my mind, The best cruising boat set up is a keel/centerboard where these is a small shoal draft keel that the centerboard emerges from the bottom of. When fully retracted the centerboard is wholely cased in the trunk and is not exposed below the bottom of the short keel. This design gives up a little performance but offers the most protection for the centerboard and represents a good compromise in performance.
If performance is your thing than a daggerboard with a bulb is a better option. (I am thinking of building a small daysailor overnighter to putter about with and will probably do that kind of a CB.)
There is more maintenance. The centerboard penants, winches and packing glands need maintenance. The pivot bushings and penant attachment points need regular maintenance and at some point replacement. There are often flaps across the centerboard slot that need periodic replacement. Centerboard often have minor damage to their fairing materials and barrier coats as the seem to be used as a depth sounder more often and there is some wear of centerboard against the side of the trunk. Even painting the Centerboard is a little harder because the boat needs to be high enough to let the whole board down.
Whether they last the life of the boat depends on maintenance and how the original board was constructed.
3) Can I sail with the centerboard partially down if I want?
Most boats can be sailed with the board partially down. One nice thing about a centerboard is that it can be partially raised or lowered, i.e. shifted in position to balance the helm in heavy air or even raised some to allow more leeway in heavy air reducing heeling. For most keel centerboarders the best performance is with the keel down for beating and close to beam reaching, partially raised when broad reaching and all the way up on a run.
4) What are the best designed Centerboard boats out there? Which ones are the boats that are to be avoided? Why don''t we see more boats manufactured with swing centerboards?...It seems like the ideal configuration for cruisers that like "thin water" anchorages.
I don''t have time to do a good and bad list this morning but keel/centerboard boats are more expenive to build than their fixed keel sisters, expecially in sizes over about 25 feet.They require more ballast and more hardware to work well. Most people seem to be willing to accept a wing or bulb keel.
5) Any other comments?...Pro''s Con''s
Keel centerboards give up a fair amount of performance over a well designed fin keel but if well designed generally offer better performance than other forms of shoal draft keels including wing and bulbs. They are harder to build properly and harder to maintain, but offer a lot of advantages to a cruiser.