Use Google Reader to find out rough estimate of RSS subscribers
RSS has been becoming an increasingly popular part of Web-based applications and services. For example, Flickr provides an RSS for your photo-stream and even a user's favourites.
Many webmasters will know just how useful FeedBurner can be to get an accurate picture of their subscribers. Using FeedBurner means that you'll have to display a specific-to-you FeedBurner address so that it can gather statistics (e.g. http://feeds2.feedburner.com/RaminHossaini) You can't really use FeedBurner though for services like Flickr, because you have no real control of what the RSS-feed-address displayed to users on your Flickr page is (unless of course, you're advertising your RSS feed on a website of your own). The "hack" described below could help:
First, start out by subscribing to the RSS feed:

Next, click on the feed to view it then click on the "show details" link in the top-right corner:

You can then see how many people are using Google Reader to subscribe to the RSS feed:

This would obviously only be part of your subscriber-base. If you're happy with just approximating it, have a look at how much of a market share Google Reader has (I've looked at a couple of statistics and it seems to be roughly 60% at the moment) and use that to calculate the unknown number of subscribers.
Finding new photos on Flickr (almost effortlessly)
There are multiple ways of finding/exploring/discovering new great photos on Flickr - joining interesting groups, adding tons of contacts, or visiting Flickr-Explore.
I feel like Flickr-Explore has the same people in it all the time (with exceptions here-and-there). Basically, if you're a Flickr celebrity and have a couple thousand people following your photos, you stand a good chance of getting a photo of your "cute" cat or a "artistic" white-wall on Explore.
There are lots of little-known users that have great photos. One way I try to find these people is by looking at what people are "Fave"-ing. You can dig even deeper by picking a couple of those faves, then looking at their personal faves, and so-on.
While doing this the other day, I noticed that Flickr allows you to subscribe to someone's fave-feed. First browse to the user's favorites:

Then click on the feed link below the faves:

Next, subscribe to the feed in an RSS reader (like Google Reader, Netvibes or Outlook)

If you subscribe to a couple of these feeds, you'll have other people doing the hard-work of finding photos for you. This works especially well if you subscribe to people that are on Flickr all the time, but Fave photos relatively selectively.
Yes, it is a lazy approach - but it's just another way of making the most out of Flickr.
Flickr modifies start page – and makes life harder
There used to be a "Recent activity" and "Comments you've made" link, which has since been replaced with a recent activity page which merges the two pages.
Here are 2 solutions.
If you have Firefox, and you prefer having the two separate links:
- Install Greasemonkey. This allows you customise the way a webpage displays using Javascript
- Install the Greasemonkey script (the link directly to the JS file is in the image-description)
Now you should have something like this:

In fact, all this script does for you is create 2 links right next to the Flickr logo with the following links (this will work without Firefox):
For recent activity
For comments you've made
So you could just bookmark those and avoid the Greasemonkey script all together.