Using jdon serialized objects as query params

Hi,

I am working with a couple of services where GET request is used for search
and some associative data needed to be passed as query params.

api.search.com/search?q=[{
<http://api.hotelsearch.com/search?hotels=[%7B>"id":"id1",
"yd2":"p1"},{"id":"id2", "yid":"p2"}]
They are passing these id maps as json serialized query params.

Here is another example, where category maps are passed as json serialized
maps.
http://indexden.com/documentation/api#searching

Are there more such examples?

Is this a standard practice?

Are there example APIs where POST is used instead of GET just because the
URLs and parameters are getting too long?

Thanks,
Unmesh