(Decided this was more of a blog than a link due to weight of text...)
From here... warning, its a long article.
Let me explain.
No, there is too much.
Let me sum up:
While SSDs (even cheap ones) provide frankly obscene sequential read/write performance and great numbers in a lot of benchmarks, most (particularly those based on the JMicron controller) are abysmal at random small writes.
And I mean abysmal. For instance, an average hard disk these days has an access time of around 13ms (for a 7200rpm drive). The best SSDs have more like 0.1ms, but the worst have an average of ~500ms. The worst case can be up to 2 seconds.
Why does this matter? well Windows does a lot of little writes in general operation, web browsing, autosaving documents and so on. When this happens it occasionally causes the whole machine to pause until the write is done.
A pause of around a second is not something you want.
Another thing to note is that new SSDs have better performance than ones that have been filled once (had their total capacity written, regardless of deletes or overwriting) as until then they always have fresh cells to write to (um, imagine making a cup of tea when you have clean cups in the cupboard compared to having to wash one up). Erasing is relatively slow, so you won't see long term performance of the numbers in the reveiws unless they fill the drive before testing.
The hit is around 3-20% depending what you're doing. Not enough to make SSDs worthless but worth considering.
Good drives:
Intel
Goodish drives
Samsung (new)
OCZ (Vertex and Summit, not core)
Poor drives
Anything using the JMicron controller (A or B, even if it has two... racing them helps little)
Um, enough summing up I guess.