Well since I upgraded some of my cameras to Nikon D800's, yes I can easliy get PSD files greater than 1 GB - especially with layers. You have a few options but I would check with your Photoshop users before taking any action. Storage is relatively cheap so you may want to consider that option first.
Flattening a Photoshop file will reduce the file size - but you run the risk of upsetting a user who wants to come back and tweak an adjustment layer or special efftects layer only to find out that is not possible as the file has been flattened and all the layers are gone.
You can also downsize the files, convert to high quality JPEG - all will reduce the file size but again is this what your users need?
Personally I archive my originals (RAW files) to two storage devices - one disk based the other I burn to DVD and my final images (layers and all) to another storage device. I often get repeat orders that may need a tweek, so I save will all layers intact. But that's just me.
It's pretty easy to get to a GB file nowadays. A 4TB drive can be had for under $200 USD. (Can store 4000 1GB files)
Things to check:
Probably no need for a layered cmyk file.
If all editing is done, files can probably be 8 bit/channel.
Eventhough PSD has a lossless compression, you may want to see if saving as layered TIFF with LZW compression makes for a smaller file.
Check trimming "big data" : image information outside canvas area.
Storage is affordable these days so buy more and don't compromise you work. If you can not budget more storage archive seldom used assets and create an offline library on DVDs.