Part of the reason my bike is so expensive is because it's very unusual recumbent bike which has been highly customized by yours truly. Many of the parts aren't even used as intended by their manufacturers (for example the frame is upside down with upside down decals...sometimes you can do stuff like that with recumbents). I guarantee it's one of a kind and looks like it.

Hopefully this alone would be enough to prevent theft? But even if that weren't enough I've also equipped it with a single quick release pedal (so it wouldn't be rideable without a replacement pedal...and even then probably not without practice) and it's too big to fit in a car (even with one wheel removed...and I have both wheels locked).
So no matter what kind of lock I use any potential thief would:
1. Need to do some work to make it rideable.
2. Need to either walk the bike off or stick it in a van.
3. Still end up with a one of a kind bike that'd require a lot of attention to sell...unless it were parted out with some difficulty (and even then the only common parts are literally the fork, bottom bracket, and headset).

Frankly I'm more concerned about vandalism than theft. It seems that there's a direct tradeoff between the two:
-Unusual bikes are less likely to be stolen and more likely to be vandalized because being unusual tells the vandals you care about your bike.
-Bikes parked in conspicuous areas are less likely to be stolen and more likely to be vandalized than bikes hidden in alleys because they're more likely to get the attention of vandals in conspicuous areas.
-Well locked bikes are more likely to be vandalized than poorly locked bikes because being well locked tells the vandals you care about your bike.

What do you think?

My daily-commute sort of bike is a folder with a chain. It gets folded up and comes in with me and when it can't it gets folded up and hidden and locked behind a dumpster or a bush (can't do that with a u-lock!).

There ya go... In my 40+ years in police work, I have never even heard of anyone stealing a 'bent. Thieves are not (generally) bicyclists, they are crack addicts. They want quick money so they can go out and buy another rock or two.
The pawn shop owner wouldn't want one; it'd sit on his showroom floor for eternity. And your crack dealer wouldn't either; he'd never be able to sell the thing.

I think the above is a good thing to keep in mind. Yes there are skilled thieves and yes all locks can be cut with the proper tools, but if you lock your bike up in a heavily populated public area where it is easily seen the risk of bike theft is going to be drastically lower (well that's my logic). I know when I bring my bike to school tomorrow (which will be the first time it'll be locked in an area that isn't specifically supervised by video surveillance (we have two bike garages that I don't have access to this term) it'll be locked right infront of a light rail stop and right outside of my school's bike shop which has floor to ceiling windows. I figure, there are people standing around that area all day long, occasionally there are public transportation police there, there are bikes much nicer than mine regularly locked in the same area, and it's in full view of people working in a bike shop.

Woah, chucky, is your 'bent a single speed with a rusty chain?

No it's an 8 speed internal hub and the chain isn't rusty yet...takes about a thousand miles of rain before the rust starts.

Chucky, how obvious is it that the lightweight is aluminum, do ya tink? Especially if you get in black and remove decal, if you can. Can you? They shouldn't use a round key, as that alone may attract marguinally knowledgeable crooks. We need a rich guy to get an old steel frame and try and break that lock with leverage. So it's been a year. what did you do?

The wisest words said so far. I've been using a cheapass cable lock that stops 90% of ppl. It keeps honest ppl honest and opportunist thieves away, but it'll bend over like ***** for a casual/amateur thief (let's just say this amateur set composes an additional 9%). I could buy a cheap Korean brand u-lock for about $10 here, but even the casual/amateur thief can break it easily. I mean, you get what you pay for and a $10 lock can't be very strong. Even a cable lock is $10. That's why I'm getting a Kryptonite Faghettaboutit for the frame and a Hiplok chain lock the front wheel and frame. This heavy combination will stop all but very clever, very determined professional thieves...the 1% if you will, hahaha. Yea, it's gonna be heavy to tote around. Maybe for shorter time periods I'll just use the chain lock. I will take my bike inside the bank or the bar with me and just lock the frame and front wheel with the chain lock (cable for now), but for when I cannot bring it in with me and I'm inside for longer than 30 minutes...I think the weight penalty is worth it. I know it won't stop professional thieves but it'll buy me some peace of mind and keep me from going out and checking that it's still there every 10 minutes.