Actually I does not affect accesstimes. Accesstime is a sum of the arm used for reading data (inside the disk) moving to the correct place, and waiting for the disc to rotate to the correct place for reading to be able to start.
RAID 0 increases the throughput of the drive, since generally the bottleneck in terms of disk performance is the disks ability to read and write. To bypass this, RAID 0 works by either splitting the stream data and (simultaniously) writing half on one disk, and half on the other, or reading from both disks and combining the data. Theoretically this would double the performance (though in practise the differance is usually alot smaller).
And as mentioned, you double your chances to lose all your data through disk failure, as either disks failure will mean files can nolonger be combined from the two sources (half of each file will be missing).