I've procured a second SSD for a venerable Lenovo R500. The specs on this notebook are pretty reasonable, but with a 6 cell battery it's lifespan wasn't great. An upgrade to a 9 cell battery gave it a boost but not a huge one. Installing an SSD made a significant difference. 6 hours of battery life is easily achievable while using the net or office productivity applications. Speed hasn't really been such an issue with this particular laptop but now it's even better.
For high end gaming rigs SSDs are the norm and even in servers now we're seeing them more often. I've changed the set up in my desktop PC - boot from an SSD, with a 2TB SATA disk for data. As the price for SSDs continues to drop they are definitely worth considering for even lower end applications. My two older laptops now are going to be useful for longer and perform better than they ever have before. Consider it for your older SATA capable notebooks!