I did a full review with photos here:
http://www.eurobricks.com/forum/index.php?showtopic=26804&hl=

AND a full review of the alternate build with photos here:
http://www.eurobricks.com/forum/index.php?showtopic=26880&hl=

(B4 saying this wasn't helpful, read both full reviews.)

Here is the closing of the review. CLOSING FOR THE ALTERNATE IS RIGHT AFTER:

Issues
Besides the whole not-being-authentic-to-a-real-bike, nothing except the kick stand. while very beefy looking, doesn't seem to hold up the bike very well. Really wobbly.

Final thoughts
I think this is a must buy. I would buy another just for parts if I could get it at the price I paid. $69, which is what it goes for now is OK if you don't already have it. Good for the tires.

To see the full size pictures, please goto my flicker site: Street Bike Pictures

My rating:

Playability: 4 out of 5. Works like a toy bike. I wouldn't fling it down the stairs, but its good.
Design: 4.5 out of 5. So close. They should make a UC version of this. :)
Build experience: 3 out of 5. On a technic scale. It's a little harder than the snow mobile. But you don't need to be in high-school to build it.
Overall: 4.5 of 5. Buy it if you like bikes or a good technic set.

ALTERNATE REVIEW CLOSING:

Features
No suspension like the first bike, but the wheels turn, the handlebar swivels, the rear tire turns the chain and moves the engine pistons.

Final thoughts
Wow. I never thought of building alternate sets. This one came out so well, it could've been the main set. I did notice that it required alot less pieces. That in itself is unusual. Normally you build the set, and find extra pieces to make the alternate. This one, I think I had exactly the parts for the main.

My rating:

Playability: 4 out of 5. Works like a toy bike. I wouldn't fling it down the stairs, but its good.
Design: 5 out of 5. So close. They should make a UC version of this. (updated. It's higher now because the alt is that good.)
Build experience: 3 out of 5. On a technic scale. It's a little harder than the snow mobile. But you don't need to be in high-school to build it.
Overall: 5 of 5. Buy it if you like bikes or a good technic set. (updated. It's higher now because the alt is that good.)

I saw some folks in GCR (Greater China Region) doing a review on 8420 Street Bike recently, that reminded me of this old set which I got quite sometime ago. With a engine, gearing system, and suspension mechanism, plus many parts (such as the two big wheels) which are not available else where, it is a great set with great playability.

This red Lego 8420 Street Bike in my opinion is one of the best set of Bike (or may be one of the best Technic Set) ever made by Lego.

Many reviewers had shared many info on the set, I think I better share some photos at my blog, which I hope will help you visualize the value of this set:

http://brickand.me/2009/07/13/Lego8420StreetBikeAGreatModelWithFeaturesNotFoundInRecentProductLines.aspx

Got this 2005 set on eBay for only €26,61. Won the bid with only 3 seconds to go! Although it took more than 2 weeks after the bidding to arrive, it was all worth the wait.
It's big, it's red, it's cool and the building is absolute fun.

Pro: Fantastic model to build. Hours of fun!
Con: no model to play with, only to display!

This was my first technic set ever and I loved it so much! It took me about eight hours to build, but it was so worth it! First of all, it comes with a working V-4 engine, powered by a working gear system, cool wheels, chains, kickstand, exhaust pipe, sleek plates, and best of all, a piece of RARE and WORKING and METAL suspension! Oh man, you should see how the suspension takes all the bumps! It looks extra cool and realistic! Also, the wheels came pre-built, so I didn't have to do anything with it, just put it on! And yes, the bike can steer. Yes, this set is perfect... except for one little thing. It was missing one of those black L-like pieces, and it took two months to find a replacement.

Anyhow, this set is perfect. At $69.99 CAD it is a great deal considereing everything you get. I recommend this to any Technic fan.

As a motorcyclist myself this set had to be in my collection, The details are almost spot on, the single sided rear swingarm is well detailed though the chain drive could (with modification maybe) be lengthened as to connect to the back of the engine/gearbox.
The engine layout is well designed and the bikes looks are well proportioned.
The only down point is the front single sided fork, can not think of a superbike with this arrangement on, unless LEGO know something I don't, the wheel and tyre design is very good.
The set's alternative model looks ok but not to my style.
Well worth the £15 spent on ebay.