Description: As the new shape of speed, the P3 sets the new standard in aero bike design. It's revolutionary seattube design shields the rear wheel 42% better than any other cutout, thus optimizing aerodynamics. Available in 650c and 700c. UCI and ITU legal.Weight: 3.1lb (55cm)
I love my P3SL - I've had it since early August 2004. This bike is a rocket! I run a 55 X 42 - alongwith a ZIPP 606 wheelset. I'm getting faster as I get older (47 years of age) - using this type of equipment. September '06 rode a 55:19 40K TT -- 2 min 30 sec faster than the previous year (ZIPPS certainly helped). It is incredibly stiff - awesome power transmission, and even with two spacers on the stem I'm way more aero than I've ever been. It's a pleasure to ride into headwinds. The only blight on this bike is the reversible seatpost -it's a pain in the ass to flip it around easily i.e. I like to ride it way forward for duathlons, but need to flip the post around to make UCI legal distance from tip of seat to centre of bb for road TT events.  
Its a fast bike. Test rode a couple 700c and they are quick. Very easy to get in a good position.
I tried Lappy's but he rides a 650c and I kept on hitting my knees on the handle bars. The 650c is great for anyone under 5'2" but like any 650c, it looks like a kid's bike. 
Own one. Really like it, comfortable, is fast, and handles well. Broken my time trials records, but may be due to higher level of fitness and new race wheels. 
Leave it to the experts. Cervelo finally put it all together, with their best bike yet. Keep all the tubes small with perfect aero shapes, without sacraficing stiffness or strength. Make all the parts aero, even the integrated seatpost, and rear stays. Keep the rear wheel tucked in hidden.
Keep the bike super light. Put the rider in a good aero position without being too low. This is the best aero frame currently on the market for the best price. Finally a Company that really knows what it's doing. No hype here. 
I've had a Specialized Transition, good but not that stiff, than a Quintana Roo Volt (650c) good and much stiffer.
But since one year I ride a Cervelo P3 and this is the best bike I've ever seen and ridden.
It is very stiff at the bottom (bracket), and I am about 5 minutes faster on a 40k bike course, it is really amazing.
My P3 is set up with Shimano Dura Ace and I have Rolf Vector Comp training Wheels and Spinergy REV X (650c) racing wheels.
I have never ridden a bike so comfortable and had the feeling that all my effort is moving me forward instead of losing energy because the bike isn't so stiff. This bike is really the best and looks really cool.
Cervelo, thanks for the design and production of such an AWESOME bike.