[quote user="JohnDuncan"]I presume that (since the glasses weren't red and green) the glasses consist of perpendicular polarised lenses[/quote]
Yep, thats the basics of it. Depending on the system they used, it could be projected by multiple projectors each projecting a slightly different version of the same frame at once, each with separate polarisation (like in 3D IMAX) or a single digital projector at higher frame rates where alternate frames have separate polarization. The screen usually has to be specially reflective so as to reflect light specularly instead of diffusely so as to maintain the polarisation.
Beyond that, the exact method varies a fair amount between the different systems available and so depends on the format of the cinema and film you saw.
Did you notice that the effect was reduced/distorted when you tilted your head? if so then that can cause a kind of sickness fealing or head ache, and is a symptom of the use of linear polarisation. Some newer systems use circular or eliptical polarisation which eliminates this problem at the cost of slightly reducing the effectiveness of the 3D glasses.
I believe that 3D TV works differently (and doesn't need glasses), and the screens that I saw at Castleford Xscape appeared to work by using small prisms in front of the pixels to split the image into multiple directions, and only really seemed to work properly if you were standing in a position where 1 eye was in the path of 1 of the split beams, and the other eye was in the path of another. It resulted in a fairly blurry (and headache inducing) image which distorts as you move around. I didn't recognise the brand of the screens so the 3D tvs from the big name manufacturers that Clare mentioned above may be better, but the ones I saw definitely didn't look good enough for the mass market.