Warning: this is an opinion. There are many others like it, but this one is mine
I work for a data storage company in a performance measurement group, so I have a pretty good idea of what I am talking about. I have been known to be wrong though...here goes...
The short answer:
The killer app for SSDs are random reads. Sequential reads are also excellent. Writes are decent. Harddrive access for video editing is generally sequential reads since mostly your machine will be reading lots of files and occasionally writing out a new file. RDD (rotational disk drives) are terrible at random reads, worse at random writes, but good at sequential reads and writes. So, for video editing, SSDs will help some, but probably not as much as you'd like.
The long answer if you care:
RDDs are good at sequential reads and writes since there is no break in reading for the disk head to move. You end up being limited only by rotational speed. Random operations are slow because the disk head has to seek across the disk looking for the correct track. SSDs are much better at random operations because they have no moving part that must seek. They are especially good at random reads because the memory cells do not need to change state to have their information read, and usually the parts of a file are striped across memory units so that parts can be read in parallel. Writes are slow for SSDs because to write a block it must first be erased, and usually, to erase a single block a group of blocks must be erased, therefore the whole group of blocks must be read, erased, and rewritten with the new single block changed. The drive manufacturers play lots of tricks in the firmware depending on the models, so check out lots of reviews to see how they perform before buying.
The best enterprise scenarios for SSDs are webservers, databases, etc. The best scenarios for desktop users is the primary OS drive. Since SSDs are good at random operations, the day to day file and operating system activities will feel much faster since parallel (random) operations will be quicker.
If you are using a desktop as opposed to a laptop you will probably be much better off getting a second RDD to use exclusively for video scratch (which will leave the main drive for the OS) than getting a SSD since the price per gigabyte ratio is so high for SSDs. If you are using a laptop for editing, an SSD might be okay since your OS will benefit so much. Still, for the money you are probably better off using a USB harddrive as video scratch space and saving your money for a better processor or more RAM.
Eventually prices will come down and none of this will matter, but for me their are not worth the money yet. You may be rich though