Trackers can increase your PR

Getting backlinks (links to your site from others) is necessary to increase your Page Rank in the long term.

Google bots are quite busy. So it is useful to have a page listing all your backlinks to tell them what pages they should analyse. That's why I recommend to dedicate one page of your site to list the pages linking to your page - I say page and not website in purpose-.

But if you're using spamming on blogs, forums and other websites to get backlinks, it would be better to keep track of those backlinks elsewhere than on your website.
Because if your website is linking to too many sites that are not related you may suffer from a downgrade backlash from Google.

So the best tool to keep track of those backlinks (the referrers) to my viewpoint is

Have a look to the tracker created for this blog: My Tracker

All my referrers are listed. When Google bots analyse this page they collect the links. And when they crawl (analyse) them later, they will find links to my blog. For a website it would be better to have a tracker for every page, but for a blog it's easier with only one.

NB: not many backlinks on my tracker because I'm not actively promoting my blog, this blog is indeed a kind of non-lucrative initiative. ;-p

Extreme Tracking has some credit with Google bots, because it's an old domain (the older your domain the better). So the tracker you set up may get a good PR with time (so put the keywords you are competing in the tracker's name when you create it !).

Other aspects of trackers:

Trackers also allow a better understanding of your visitors: you may know the referring link, the keyword used in the search engine and much more.
Data-mining may help to improve your website.

To keep track of your visitors, here below a list of free trackers (but not for SEO):

StatCounter Invisible, no Ads :-)

Activemeter Invisible, no Ads :-)

Motigo Webstats Logo + PopUnder Ads :-(

I strongly recommend the invisible counters. Unfortunately even if Motigo is user-friendly it cannot compete because of those 'damned shit' PopUnder ads.