Disk drives don't affect processing speed - that's the CPU.
An SSD in a laptop should speed up booting (especially on something with a good CPU, like an i5), and program loading.
Whether it's worth the cost is something you have to judge for yourself, but given that you are likely to boot a laptop more often than a desktop, I have every intention of getting an SSD in my next laptop.
BTW: depending on the chip set in your laptop, you may not be able to get any significant advantage from a SATA III SSD, so you might as well choose from the SATA II SSDs - they are significantly less expensive. Maybe that makes it more attractive?