It sounds like it's lacking TRIM/wear leveling support. The problem with SSDs is that they're a moving target - the technology is still changing.
On a standard hard drive, when a block of data is marked as erased, it isn't really erased unless it's over written. When a block of data has been marked as erased, it's block identifier is put into a queue, and the next time a write operation is performed the OS will search out the most sequential list of available blocks and use them. If the IDs that had previously been marked as "erased" it means they're available and the OS can over write them. This is why if you want to make sure no one can recover your data you need to zero the drive, because that will overwrite every single sector on a hard drive with binary zeroes.
This is not the case with SSDs. When a block of data is marked as erased, the drive has to first identify the block, then erase it, and THEN it's available for use...it isn't just readily available like it is in a regular hard drive. Typically what seems to happen on the older SSDs is that they actually don't start actually erasing and zeroing any of the blocks of data until they've all been used once. At that point, every time a write operation takes place, it first has to physically erase the block(s) and then write to them. This is time consuming and slows the drive down.
If the drive has real TRIM and/or wear leveling support, what will happen is that as blocks of data become marked as erased, rather than waiting for the drive to cycle through all available blocks, it runs a low priority background process that will "clean" the previously erased blocks with minimal interference to the user. Wear leveling keeps track of the usage of each block to ensure they're all getting used evenly (hence the "leveling" in wear leveling).
As I said, SSDs are still a moving target. TRIM and wear leveling is only supported on Mac OS X in some drives and some OS versions. If they aren't adequately supported, I believe the process is to clone the SSD to a regular hard drive, completely re-initialize the SSD, and then clone it back from the hard drive to the SSD.
I'm going to steer clear of SSDs until all the kinks seem to be worked out. This is one of them, but another one is where an SSD just "gives up the ghost" and seems to do a complete re-initialization on itself for reasons known only to the SSD.
Keep good backups!