Brooksbaseball.net has a great Pitch F/X tool. So, building on the fanpost by Desert Ranger, I've copied some of the information from the Brooksbaseball.net site that shows Harrison's four-seam fastball has a lot different movement on it now than in the early part of the season. In fact, his four-seam fastball movement is looking quite a bit like Holland's, though without the velocity.

Another difference between Holland and Harrison is that Holland's slider follows a path similar to his fastball until about 20 feet from home plate. Harrison has no pitches that follow a similar path.

Matt Harrison's Four-Seam Fastball Statistics
Date of Start	Average Speed	Max Speed	Average H-Break	Average V-Break	Number Thrown	Strike Percentage	Nibbleness	Time to Plate
4/17/2009	89.56	91.8	5.82	9.52	53	60.38	5.49	0.411
4/22/2009	91.73	94.8	5.88	9.45	44	59.09	4.60	0.410
5/3/2009	89.92	94	8.94	7.88	45	62.22	5.37	0.408
5/8/2009	93.15	97.7	9.18	7.66	92	67.39	5.77	0.433

Derek Holland's Four-Seam Fastball Statistics
Date of Start	Average Speed	Max Speed	Average H-Break	Average V-Break	Number Thrown	Strike Percentage	Nibbleness	Time to Plate
4/22/2009 (2.1 IP)	94.40	97.1	7.37	9.45	36	69.44	7.94	0.399
4/25/2009 (3.0 IP)	93.57	97.1	8.45	7.76	39	53.85	6.14	0.402
5/6/2009 (2 IP)	94.05	95.4	9.45	7.53	15	80.00	3.77	0.400

Brooksbaseball.net Pitch F/X tools for Matt Harrison starts:
4/11/2009
4/17/2009
4/22/2009
4/27/2009
5/3/2009
5/8/2009

Brooksbaseball.net Pitch F/X tools for Derek Holland's outings:
4/22/2009
4/25/2009
5/1/2009
5/6/2009
5/9/2009