Will a single cylinder be enough?

I currently have a 1200 Buell and I want to get a cruiser or standard bike. I have my eye on a Suzuki Boulevard, and I really like the little S40 (roughly 650cc). The main downfall of this bike (IMO) is that it is only a single cylinder.

I plan on using it mainly for commuting. I also want my girlfriend to ride on the back every once in a while for recreation on the weekend.

I weigh 145lbs and she weighs about 115lbs. I would expect us to get to highway speed often. Do you think this bike would be enough to hull us both around?

Yes.I had a friend who owned a 1978 SR500 Yamaha single.He weighed 275lbs and his girlfriend weighed 200 and they got around just fine.It really depends on a person's preference.

When you say HIGHWAY speed, are you talking 70 + or? It will do that with two of you,
but a 750 or 1100 would be better if you plan on lots of highway riding.

It should be quite adequate for the need you state. The single cylinder is OK, it just is not as smooth as a multi-cylinder, but it also cost about half the price when you tune it up!

Should do what you want
Saddle up & go for it

They are all enough. Half the world commutes families of 4 on 50cc scooters. You gotta ride the thing yourself to see if it is to your liking, but as far as practical commuting it is overkill.

1200 Buell hp 103
S40 30hp

It will be much weaker than the Buell, but perfect for commuting.

I once met two canadians who were riding 70cc honda's at Zion national park in Utah. Their goal was to keep going until there was no more roads going in that direction. They had tents, sleeping bags, food and spare parts. I often wonder just how far they got. They were still having a blast. Its not the size of the motorcyle, its the size of the grin on your face.

The fact that the engine is a single cylinder "thumper" is less important than the power to weight ratio of the bike. Vibration/ride comfort may be more of an issue, although not having ridden that particular thumper, I can't say for sure. I am fairly sure that you will be disappointed compared to your 1200 Buell as far as acceleration goes.

It should haul the two of you without any problem. After all, once upon a time, a 650 was considered a pretty decent size bike.

All the above answers are excellent.
I have a 100 Horse power four cyl in the garage...but what did I ride today on this beautiful Spring Day ? My 500cc Single Cyl "thumper". And I an 6'4" and weigh 255lbs.
My buddy I rode with had a HUGE 650cc Single.

The two of you combined are the weight of an average cruiser rider so no problemo.