I'm a web geek, not a designer, so I'm not usually producing the original InDesign document or creating the PDF, but I get a lot of bloated PDFs sent to my inbox for posting!

As a general rule, before I post to the Web I open *all* PDFs in Acrobat and run “Document > Reduce File Size…” In almost all cases Reduce File Size further reduces the size of whatever anyone sends me and I've had no problems with readability.

Sometimes, if the PDF is especially bloated I may go to Advanced > PDF Optimizer, but Reduce File Size usually is good enough.

If you do use Advanced > PDF Optimizer, I second the recommendations for 150ppi for color images and 600ppi for monochrome as producing a decent sized PDF that can still be printed without looking terrible. You can even go to 300ppi on monochrome if you aren't too worried about print quality.

In the old days (!!!) I'd sometimes go with 72-75ppi for color images, but with larger screens being common I don't recommend that anymore, because even at “Fit to Width” size in a PDF reader, the image is probably scaled larger than 100% on your screen. The images still look “okay” at 75 ppi, but not crisp.