They should check your valve adjustments and retorque your head bolts.  This requires exposing the top part of your cam by lifting the top part of the head off and requires removal of gas tank, etc.

Many problems are traced back to this first major service as the techs are NOT familiar with your engine (unless you specifically ask for a tech that has done it before many times and get assured that the older, experienced man will do your work).  TELL THEM YOU WANT SEALANT PUT ON THE LITTLE RUBBER PLUG WHEN IT GETS PUT BACK IN AFTER TORQING THE BOLT NEXT TO THE EXHAUST HEADER.  (their shop manual doesn't tell them to do this and when they don't do it, you get the infamous head oil leak within 10,000 miles or so).

Good luck -- we get more reports of bikes getting messed up at this 600 mile service because "Hey kid, go do the 600 mile service on this here single cylinder -- that's about your beginner speed (hee hee)".  

They give the kid the standard 2.6 hours to do the whole job and he struggles through it, putting oil filters back in backwards and leaving pin/keys off cam gears and not putting sealant on plugs and putting cam seal rubbers in backwards and blocking off a few oil passages with excess goop ......

It is not a simple job.  The kid will mess it up -- he has no experience working on this bike.  The kid will follow "the book" and the book doesn't tell him to do critical parts of it as the book is incomplete.

Oldfeller

I will be the counter balance to oldfellers post.  I checked with 4 different dealerships and went with the one that had 'almost' the best price but that I also felt 100% comfortable that they would take care of my bike.  That was about 1200 miles ago and I have not had a single issue.  If I had it to do over again, I would take the exact same route.  Sure there are cases where the initial service might get goofed up and cause some issues, but I highly doubt that it is 'normal' for your bike to come out in worse shape than it went in.

Nope, I'd suggest doing it yourself.   When we do these things they rarely go bad on us.

I did my 600 miler myself, with the Clymers and the postings on the tech docs section. Although I did not find any valves out of adjustment I did find one at the upper limit so I adjusted it to the center of the spec.
In addition to torquing the head nuts, you'll also check the free play in your brake & clutch cables and your automatic decompression system. None of the work is really hard if you have moderate wrenching skills and a good torque wrench. It also helps to have deep offset metric box wrenches.

Everything went smoothly and my bike runs great. I use it to commute 25 miles to work each day, and so I wanted to make sure it was done right.  It is a good way to get familiar with your bike, and since you'll be re-torqing the headbolts a few times in the future, it's a good time to get some practice.

I think that should work fine for you.  Be sure you keep track of where each head cover bolt is removed from since they are not all the same.  And as mentioned, seal under the head plug cap as well as the head cover mating surfaces.

Be sure to reward yourself with a six pack and a new fishing lure with the $300 you save. Ok. Make it a 12-pack and a new rod...

If I had a brand new S40 waiting for the first maintenance I doubt I would remove the head cover and retorque the head nuts at all just because there may be leakage problems in the long run. It's supposed to be done every 6000 kms which I did for the first few years but eventually the cover started to be harder and harder to seal properly. After 8th time I decided that's it and haven't touched the cover nor the bolts since.  

300 talk about over inflated.