Slitherlink or loopy puzzles...

I have seen slitherlink puzzles, or loop the loop, quite a few times in the past but they have never really appealled to me.

However I have started doing some of the easier ones recently and to my surprise after getting confused with the first few puzzles I am actually starting to quite enjoy them.

As you go through you start to spot patterns that aren't immediately obvious but once you think about them you start to realise there are only certain ways of marking cells when those patterns occur, for instance when there are two 2's diagonally then whilst you might not think that is helpful it actually is! And when there are two 3's adjacent to each other you can mark three lines immediately as far as I can tell.

It would be interesting to hear what other people think of slitherlink and any useful patterns that you can use when solving them.

The other thing I would like to know is if the puzzles ever require you to basically guess, or is there always a way to work out in a puzzle how the loop must go if you have made all the possible deductions up to the stage you are stuck up? With some puzzles I think the only way is to make a guess and then see if it works or not, but that doesn't seem that satisfying so I wondered if that is the case or not!