Jump on the Intel 330 180gb.
Larger ssd's perform a bit better. Yes, a SSD slows down as it nears full capacity usage.
The reason is that the ssd has to work harder to find unused nand chips so that it can do a write only.
Otherwise, it needs to do a read/rewrite operation.
In sequential operations, there are more nand chips that can be accessed in parallel with a larger ssd.
Sort of an internal raid-0.
From a reliability point of view, I think Intel and samsung have a better shot.
They both make their own nand chips and can do a better job of validation.
A SSD is 50x faster in random i/o, that is what the os does mostly.
A ssd is 2-3x faster in sequential.
It is one of the best performance upgrades you can make today.