They say they slow down with time.
That was mainly a problem with older SSDs that didn't support garbage collection or TRIM, or, when SSDs were used on systems that didn't support TRIM such as Windows XP. Newer SSDs typically support TRIM and have firmware that supports garbage collection on systems that don't support TRIM. It's not all rosey, garbage collection can shorten SSD life while TRIM has some shortcomings and overhead if it's used for every file delete. But on newer systems and SSDs that support SATA 3.1, there is a new Queued TRIM command that eliminates that problem. With Windows 8 which supports SATA 3 natively and a SATA 3 SSD, I wouldn't expect this system to have any problems at all in that regard unless the SSD is filled. Just like a standard drive, you need to leave some free space and not fill them up.
The system can still slow down over time anyway, but it's less likely to be caused by the SSD.