After reading this question, I was wondering: is frequency hopping considered ``the most effective use'' of the frequency as stated in the FCC regulation?
If so, is there any restrictions on how the hopping should be performed?
To answer your second question first:
The FCC doesn't regulate the use of frequency hopping within the amateur radio spectrum. The band plan has suggested modes of operation, which don't include mention of frequency hopping, within the amateur radio spectrum, but also include many "experimental" allocations where you could engage in any form of frequency hopping you might want to attempt.
As far as whether frequency hopping is considered the most effective use of a given chunk of bandwidth, the answer is no. No one officially states or implies that frequency hopping is a particularly effective or most effective use of a frequency. Depending on what form of frequency hopping you use, you may be able to more effectively or efficiently use a frequency than with some other modes, but not always.
Note, however, that the wording is very subjective, "most effective use of the amateur service frequencies" doesn't restrict users from consuming a 25kHz FM channel with slow morse code, even though one couldn't easily prove that this is the most effective use of that frequency. It may be that they should be using a different mode, but it's possible that they're running an experiment that is most effectively carried out in this manner.
There is a wide range of what might be considered most effective, and as long as people aren't regularly abusing the spectrum we're given, there's little need to try to force "one true way" on the community, and add artificial restrictions to stop theoretical problems.