Up until recently, Picasa Web Albums had a 1GB per-user data cap, but now, G+ users can upload any photo smaller than 2048x2048 or video shorter than 15 minutes without it counting towards to the 1GB cap. Fortunately, if you upload your photos with G+, they are automatically resized, so they won't take up any space in Picasa, whereas photos uploaded directly to Picasa will be unaltered, regardless of size.