Caution on OCZ vertex. There are two versions out there, 34nm and the 25 nm. The 25 nm version have problems. It appears that the # of problems seems higher with the OCZ line recently. Intel has the higher reliability rating, but slightly lower performance. Not sure if this is true for the newer Intel Sata III SSDs as they use a marvel controller, and again their performance is lower, and this may decrease reliabilty - UNK, only time wil tell.
On size. I know that there are some that use 60 and even 40 gig SSds, But the recommended min size is 80 gigs. With less than 80 you will be limited in number of programs that can be installed (win 7 takes about 16 gigs all by itself). Plus it is recommended that you leave 10->15% free.