The Savage LS650 (now the Boulevard S40), is a single cylinder, 652cc bike, and people commonly refer to this bike as a "thumper".
Acceleration is fairly strong in the lower gears, and the power band is fairly broad. Once the bike hits about 65mph, acceleration slows down, and you can expect to top out from 85-95mph. The bike does have fairly good passing ability on the freeway, and is great for around town cruising. The bike has a rated HP of 31, 33.6 ft/lbs of torque.
The bike has a wet weight (gas, oil) of about 380lbs, making it about the lightest weight bike for the size of engine you are getting. Due to the lightweight nature of the bike, it is extremely maneuverable, and is great on tight curves!
Braking is quite good, with a front disc, and a rear drum brake. This is largely due to the low weight of the bike, and its relatively low positioning toward the ground.
One item to note is that most people (including myself) have found that the Savage tends to have backfire (generally mild) on deceleration (this is due to Suzuki making the bike more EPA friendly to meet the requirements with its carburation). Simple modifications to the carb can completely take out the backfire, and exhaust upgrades can also help with this issue.
The bike has a wonderful cruiser style to it, and up until 2004, before the bike changed to the S40, it came with the sissy bar and back rest, as well as the buck-horn bars. Suzuki had intended this bike (I believe) for people of shorter stature (generally under 6ft tall). Myself, I am 5'10", and weigh just short of 200 lbs. I find that the bike fits actually pretty good. Some people have noted the buck-horn bars not being their cup of tea, so they change it out for a straighter type handlebar. The bike has some chrome on it, but its not near as generous as some of the larger bikes out there.
The seat, while fairly large, is fairly uncomfortable after about 30-45 minutes of continuous riding. A gel seat is definitely recommended for longer rides. Also, the pillion seat is quite small, and your passenger may complain of being too cramped. For taller riders, you might consider having highway pegs put on the bike, so you can stretch out a bit.
The Savage has always been touted for its high rate of reliability. This can largely be attributed to its belt drive, its single cylinder (thus its single carburetor, and no need for synching with other carbs), and its relatively uncomplicated design. With a Clymer manual in hand, regular maintenance is a simple thing to do, as well as minor repair.
Unfortunately, aftermarket products are relatively scarce (but not near as bad as they use to be) for the Savage, as many people view the bike as a "beginners" bike (certainly not always the case!). Fortunately, eBay offers the Savage owners a lot of options, from exhaust upgrades, to gel seats, to handlebar change outs, to dressing the bike up!
The bike sports a 2.77 gallon tank, with a reserve capacity of 0.66 gallons. On average, I get about 55mpg, and have to fill up about every 145-155 miles. If you ride real hard, you might only average closer to 50mpg, but I have read some people getting over 60mpg. To add to the cost benefit, a brand new S40 will run $4300 MSRP, but can be had through many a dealer for under $4k. If you buy used, like I did, you can often get a Savage for under $2500! For a 650, this is really a great deal!
A really neat bike, especially for someone new to the world of bikes. Even experienced folk will enjoy its playful nature, and appreciate its great maneuverability and gas savings! A highly recommended bike!