I know LJ isn't really intended as an RSS feed reader, but I never really realised just how much it isn't. With LJ, you pretty much have to read your friends page linearly. I would reload my friends page every day or two, and keep hitting "<< Previous 25", opening each window in a new Firefox tab, until I reached the point where I last left off. There isn't any indication about where you last read, so you need to either recognise the older posts or remember to have a quick look at the most recent post before you hit Reload on the first page. Then, you scroll through each page of posts reading everything. If you don't read it when you see it, you'll never find it again. If you find a long article that maybe you want to read later, you need to make a note of the URL or open it in yet another browser tab or something. I can scan stuff pretty quickly, so this whole process maybe wasn't as bad as it might sound.
I subscribe to (as of last count) 60 RSS feeds. Some are more active than others, but a typical day would produce two pages worth (ie. about 50) new posts between my LJ friends and the RSS feeds. If I didn't read LJ for a day or two, the backlog adds up quickly. After not reading LJ for several days, the backlog simply becomes too much and I miss stuff.
Enter Google Reader. After removing all my RSS feeds from my LJ friends list, the daily friends page reload is much shorter and I can easily skip a day or three without having to load up multiple pages of previous posts. All the RSS feeds I read are nicely organised by Google Reader and I can pick and choose what I want to read at the time. It's just as easy to plow through everything that's new, as it is to only read the more interesting feeds and leave the others for later (or even "catch up" on them and just mark all the new stuff as read). And Google Reader has keyboard shortcuts that I didn't think were possible in a browser, which makes it really nice to use.
LJ's RSS support was fine when I was just reading a few RSS feeds. But with the number I have now (which I don't think is terribly many), it just doesn't scale. Google Reader does a much better job.