I replaced my laptop hard drive with a 120GB SSD about 6 months ago, it made a big difference to boot times and program start up times. Mind you, a fresh installation of Windows also helped I'm sure.
At the same time I replaced the laptop DVD drive with the old 250GB HDD. That now holds all my documents. Bought the SATA adapter on ebay. I now have my DVD drive as a USB connected external drive that I hook up when needed, which isn't very often. Again, I bought the external DVD case on ebay.
Windows 7 Home 64bit operating system and all programs are kept on the SSD, and all documents, downloads etc. are kept on the HDD It all works very well, the only problem that occurs infrequently seems to be associated with viewing video clips online. Youtube clips seem to have some sort of caching issue with the SSD and cause the system to hang requiring a restart. I suspect it's some kind of caching issue, but it's not a huge problem for me.
The 2nd huge improvement for my laptop setup was to connect a 2nd monitor, a 19" flat panel, setup in
portrait mode. The monitor had been sitting in the shed unloved since I exchanged my desktop for the laptop. I initially wanted to use it for documents in MS Word and for reading ebooks in portrait mode, but I find I use it for practically everything these days. I use a program called DisplayFusion Pro V4.1 to manage multiple monitors. Love it! Laptop screens are OK, but the wide screen effect isn't the best for browsing the internet etc. Just having two applications working side by side without having to tab between them is great.
Cheers
Chris