50/50 really, it's not consistent so you'll have to check within the OS – but if you have the problem, you can't solve it. Issues with Nvidia chipset firmware or something weird like that. Best thing to do is click the Apple Menu at the top-left, and hold the 'Alt' key. You'll see that 'About this Mac' will change to 'System Information'.
Then click SATA/SATA Express on the left-hand side, and click the chipset above your SSD. If you look at the Link Speed, then Negotiated Link Speed. The problem on the 2008s were that the Link Speed is 3Gb/s, but the negotiated speed is 1.5Gb/s. If you've got 3Gb/s on both, you're absolutely fine.
Again, not the end of the world when you've got an SSD in, but due to the bottleneck I find that the white unibody plastic 2009 MacBooks are a
little quicker with an SSD because they don't have that problem.
It's mainly just to let you know in case you wonder why it's running slower than you'd expect with an SSD. Hope I didn't worry you, it's still very capable and will run absolutely fine, even at 1.5Gb/s.