Boot up, resume, and shutting down will have increased speeds. Look on newegg for solid state drives. The prices are now well under $1 per GB. The SSD and HDD setup is common. When you install programs that aren't write speed critical, install them to a specific folder on the hard drive, and vice versa for the solid state drive.
What you want to look for is read/write times. Look for 500+MB/s read&write. Also, sata III if your system supports it.
My personal opinion is that an SSD is the upgrade for any PC without a doubt!
Even on a system with say an older CPU like a core 2 etc. the speed difference is phenomenal. The only drawback is the price/capacity ratio, although prices have gone down you can still get a far larger HDD for the price of an SSD.
I would say that a ~120GB SSD installed as a main (OS) disk and a second large capacity HDD for storage is the best setup.
The one sure thing is that you will not be disapointed you got one!