$200 for an SSD is a far better use of money for the average programmer than say the upgrade from I5 to I7 on a 13" MBP. There are many parts of your computer which you'd spend $200 on that get you less of a general every day performance boost than a SSD.
The reality is that it significantly increases performances for all workloads but streaming videos (huge sequential reads).
Most of computer usage is random access to small files, and that's a field where SSDs utterly annihilate rotating platters (not that rotas have any advantage but storage capacity, mind you, SSDs are also superior in seq read and write, but on random we're talking 2MB/s on 4k random write for a VelociRaptor to >200MB/s for a Vertex 3; 0.68MB 4k random read for a VR to >90MB for a Vertex 3, for sequential performances the difference will be a factor of 2 or 3 tops between a VR and a top-of-the-line SSD)
The difference is, of course, even more impressive for laptop drives: most laptops don't house 10k, 10W monsters like the VRs