Do you want to be alerted when certain blogs or Twitter feeds are updated? The surest way for me to be sure see new items is to have them delivered as email messages.
Some blogs offer email subscriptions, but most don't. However, I found a way to do this even for feeds that don't offer email delivery by playing with these instructions for setting up a Google FeedBurner subscription for one's own web site: http://wordpress.jdwebdev.com/blog/feedburner-email/
1) First, you need to go to FeedBurner and set up an account. Once that's set up, click the My Feeds link in the upper-right corner.
2) Next, you need the RSS feed address for the page you want to track. Open a new tab or browser window, find the page you want to track and look for an RSS logo or link. I'll use Leah Garchik's Twitter feed of public eavesdropping as an example. On her Twitter page http://twitter.com/leahgarchik there's a link in the lower right corner saying "RSS feed of leahgarchik's tweets". Clicking on that link takes me to http://twitter.com/statuses/user_timeline/70746464.rss
3) Copy the RSS feed URL, go back to FeedBurner's My Feeds page, and paste the URL into the box labeled Burn a feed right this instant. Click Next.
4) You should see a page saying Welcome! Let us burn a feed for you. Click Next.
5) You should see a page saying Congrats! Your FeedBurner feed is now live. Click the link that says Skip directly to feed management.
6) Click the tab at the top of the page that says Publicize.
7) On the left side of that page click the link that says Email Subscriptions.
8) Click the button that says Activate.
9) You should see a panel labeled Subscription Management. Now comes the tricky part. FeedBurner's instructions are designed for someone posting an RSS feed link on a web site. But you can skip that part by clicking the link in the middle of the page that says Preview Subscription Link…. Paste your own email address into the Email Subscription Request box and enter the wavy CAPTCHA letters. You'll get a confirmation email at the address you entered.
10) Click the verification link in the email and you're done. You'll start getting email notifications when new content is published on this feed.