Recently I bought an SSD drive and I am very impressed still with its performance. Last week I installed a new 4GB stick into the laptop bring the total amount of RAM in the machine to 8GB. It all installed well and Windows happily told me I had 8GB of usable memory. But there was a considerable decrease in perceived performance.
The issue it seemed was the new pagefile that Windows was using. Because of the amount of RAM, the pagefile was now 8GB. Windows writes to the pagefile every so often but it does so using random rather than sequential writes. And due to the way an SSD handles deletions in the file system this was starting to slow the system down.
So a quick browse of the web to see what could be done. The main suggestion was that if you are using 4GB or more of RAM you should probably turn off the pagefile because the OS can probably handle the whole thing in memory. There were additional tweaks too.
I turned off my pagefile and the performance seems to be back up again. I also downloaded the Intel SSD Toolbox which has some tools for management of your SSD and for performing maintenance on the disk.
I also download and used SSD Tweak which contains a number of tools and tweaks to enhance the performance of your disk. Its very easy to use and disables a number of now unnecessary Windows services.
The above worked for me but your mileage may vary.