Hey Chummers
As an SR-GM, i suffered burnout some years ago, but my regular groups resistence to other games and unwillingness to GM in my stead makes us play the occasional oneshot. Sometimes I am craving to run an SR game, but most of the time, I am indifferent at best. Add to that, that its usually fairly spontanious, so i have little preparation time and don´t get to see the PCs in advance usually. Once I see them, they do usualy fail to capture my imagination.

This is seldome a problem when I am running any other game, give an introduction to SR-noobs od get to just play a PC.

While I fail to have the motivation to prepair a full campaign -because those usually lead to nothing after a few sessions due to party disintegration- I would like to enjoy a game with my old buddies now and then.

So how can I enjoy it? Any tips appreciated.

ASk for the PC w/ backgrounds before the game. Unless they have character ADD, they should be able to do that and stick with the same character. That may help with your prep--and do have an adventure preprepped if they want to play. Asking you to consistently GM an SR game on the fly though is pretty tough.

For spontaneous one shots--You may want to look at missions, as those are designed to be stand alone adventures.

Regarding Burnout: Hey it happens, but usually for a reason. Not sure why you are burned out, you just might need a break from GMing and want to play.

Yea, thought about trying Missions some time, after I read into the recent FAQ this week.

We play pretty infrequent, so most of the time I can motivate my self to some degree - if i have no motivation at all, i wont gm, but s.t. it just feels half-assed, at least for me. I think the PC issue is my biggest problem indeed.

Try running a different game, just to shake things up.
A few ideas:
The Dresden Files RPG (if nothing else, spending a session reading the notes in the margin is awesome)
The Serenity RPG (because nothing's funnier than figuring out that money is worthless)
Traveler* (because dying at chargen is FUCKING HILARIOUS)
Ironclaw / Jadeclaw (because everyone wants to be a dragon, a phoenix, or a stealthy elephant** once in a while)
Road Hogs (because TMNT + Atomic Apocalypse + Road Wars reaches the Rule of Cool and blast through the other side)
Brontosaurus Rex (nothing like playing cowbows in the wild wild west, on another planet, with fucking dinosaurs--hell, you can even play as one)
Scion (because sometimes all you want is to play god)
Dogs in the Vineyard (because sometimes you want to play is god's fist***)
RIFTS (because sometimes you just have to say "screw it, we don't need rules")

*I suggest the most recent version by Mongoose
**Yes, its possible to build an elephant character that's really, really sneaky.
***You really do go around punching people because you're always right (because God is on your side). The rules even say so. The GM is instructed "to say 'yes' or throw dice." An example from the one game I played:

PC (after a grueling dice match of words, where he is trying to rationalize why he and the girl he isn't married to are both in the street naked, while her house is on fire and he's losing): "The burning building collapses on him."
GM: "....alright, it does. He dies and there are no other witnesses to your sin."

Drako, dude, I´d love to!

Traveller is Awesome!!! I love it
Serenity is awesome, too - at least the show, never tried the game
RIFTS is super awesome!!! Juiciers, Magic, Demons.. what else could you ask for?
And Traveller is just Awesome -enough to say it at least twice- I love rolling up characters

The other games i don´t know - some I heard about - i.e. DitV & DF, may be not my style..

Now here is the problem:
One of these guys will not play any fantasy.
One will hardly play anything that is not cyberpunk.
The last will not play anything but Shadowrun.

I tried to motivate them for other games time and again :-/

Fortunately they are not the only RPGers i know ...

I prefer Torg to Rifts.

But I think that's cause I've got a Hardon for the CyberPapacy

Alright, that leaves us with:

The Dresden Files RPG (just needs your cyber flair; though could be too High Fantasy for the one guy, but its basically a more modern ShadowRun)
Ironclaw / Jadeclaw (you'll need your own setting; the rules are solid, but the fluff won't fit your group)
Road Hogs (Just Add Humans and you get a post apocalyptic wasteland with vehicle combat; should be plenty cybery without being too fantastical)
Brontosaurus Rex (with a stronger emphasis on technology--there IS space travel in the setting, but tends to be low key, as far as I can tell)
Scion (invent some machine gods for your cybermonkey, though might be too fantasy orriented for your "No Fantasy" guy*)
The Serenity RPG (there's enough room for "magic"/psychic powers, to please your SR guy)
Traveler (definitely psychic powers, if ungodly rare--take 2d6 and roll a twelve twice in a row)

And one I forgot:
Alpha Omega. It's a bit high-fantasy, but tends to be down to earth about it (Angels and Demons are going to war, and the battle field is Earth, and humans aren't happy about that). I suppose, if anything deserves to be called SR d20, Alpha Omega is it (they started with a d20 rule base and ended up with something that doesn't use d20s very often. As well as having a lengthy backhistory that mimics ShadowRun's).

*Tell him to fuck off and go play F.A.T.A.L. Seriously, there's no RPG that isn't fantasy.

I always find that watching cyberpunk and con-themed movies and reading similarly-themed books helps me to get over my downers.
Actually, come to think of it, SR burnout is not any different from your general burnout, and there's quite a lot written about how to overcome it (like here)