The biggest performance lag comes from using really large images and letting the theme script scale them down for you. This might work OK in your local environment, but it can have great effects for users with less optimized setups and slow internet connections. Always scale down your images to a reasonable size and use jpg for compression.
Use reasonably sized images
A good standard to start with is 600 x 600 pixels using 70 as quality and around 100 to 200 KB in size. Other standard sizes for landscape images would be:
- 1024 x 768 pixels
- 1280 x 960 pixels
Compress your images
Another good procedure would be to compress your images prior to uploading.
There're several image compression software available for the Mac, I use JpegMini: http://www.jpegmini.com
Don't add too many images at once
There are no limits to how many images you can add, but after 20 it can clog the pipes on load, especially in slower browsers like Internet Explorer.
Use a reasonable amount of images at first, then try the check/uncheck method on RapidWeaver Album to remove or add images on the fly.
Photo Album settings
The standard RapidWeaver Photo Album plugin may apply further compression to images. You may opt to improve the image quality go to Photo Album page inspector > Image Settings > Best.
Last, you may uncheck the 'Scale Images' option.
Photo Album Settings