An ELT correspondent writes to say he thinks he has a problem with the verb like. He has been interpreting such sentences as I like reading mind-tickling books as an expression of an ongoing habit, but I like to read a good book as an expression of current want, and not as a statement of habits - equivalent to I'd like to read a good book. He thinks that 'the would like form is simply more polite or perhaps putting more stress on the "want" aspect of the verb'.
His suspicions are right. Both constructions after like are habitual, though in slightly different ways, for there is a potential contrast of aspect here. ELT books tend to concentrate on tense rather than aspect, and often say little or nothing about cases like this. It's a major theme of the reference grammars, though, and readers wanting to follow up the point should take a look at, say, section 16.40 in the big Quirk grammar (A Comprehensive Grammar of the English Language).
Usually the infinitive form gives a sense of potentiality for action whereas the participle gives a sense of actual performance. To adapt one of the Quirk examples:
Sheila tried to bribe the jailor [but he took no notice of her offer].
Sheila tried bribing the jailor [but although he took the money she didn't get the result she wanted].
In the first example the jailor didn't take the bribe; in the second example he did.
The potentiality/performance contrast is clear with emotive verbs such as dread, hate, love, loathe, prefer - and like:
I like to visit Mary [whenever I can, but I don't actually get the chance very often]
I like visiting Mary [and manage to get to see her most weekends]
Transfer the contexts, and the sentences - especially the second - don't work so well:
I like to visit Mary [and manage to get to see her most weekends]
I like visiting Mary [but I don't actually get the chance very often]
It's because the infinitive has this strong implication of potentiality that the would like construction uses it for hypothetical situations: I would like to visit Mary. Here, I would like visiting Mary is much less likely to occur, and for me it's ungrammatical. The contrast is even more marked in interrogatives: Would you like to visit Mary? is OK, but Would you like visiting Mary? isn't.
Notice that the aspectual nuance varies with the kind of verb. With a verb like read (which lacks the iterativity implicit in visit) the notion of continuity implicit in the act of reading reduces the contrast, so that the following two sentences are as close to being synonymous as you'll ever find:
John likes to read a good book
John likes reading a good book
In both cases, you do read good books regularly. To get a hypothetical sense, you have to alter the construction, and that is where the would form comes in. In John would like to read a good book he has not yet done so.