A SSD is 50 times more expensive for only 2 times more speed. ( comparing a 1 TB SDD to a 1 TB HDD ).
Not worth it.
When the price / speed ratio comes down, then we start talking.
How do you figure it's 2x the speed? The 1TB HDDs transfer data at around 70-90MB/s. The first 1TB SSD that I found is the OCZ Z Drive, which transfers data at 1.4GB/s. That's about 15x faster. Also, the 0.1ms latency of SSDs is where the real benefit is IMHO. Everything you open opens instantaneously.
To me it'll be worth it when the 512GB is about $250. Yeah, I know I'll be waiting a long time. But there's no way I'm compromising storage capacity, and there's no way I'm dropping over a grand on a hard drive just so Finder can feel "snappier" and I can have a boot time that 10 seconds shorter than my already fast boot time.
Why not get a dual-drive setup? You can get a 128GB SSD which is more than enough for your OS's and apps, and a 1TB HDD for media/other data. There is the drawback that you have to use an external optical drive, but for the rare occasion that I need to use a disc, it's a non-issue.