How many entries in the hosts file? I did this on linux, osx and windows years ago before adblock was around. Due to the nature of resolving and it's serial hunt through hosts, this greatly impacted everything due to the thousands of entries. Mine also included known malware/forged sites and bulletproof hoster sites though.

If you are talking thousands of entries with no performance impact on 'not just browsing' that's very good.

Being close to and knowing the guts of how these ad networks work, I'm guessing you need to update often?

Anyway, I'm using adblock and tested with/without it and there is a slight impact, but trivial, especially with so many sites overloaded with ads now. You aren't waiting for the pages to pull in junk from CDNs it improves overall performance. Even Amazon's pages load faster.

Plus, you don't have to constantly worry about updating your hosts file.

Finally, we are seeing more and more ERMs show up and just idiots that pull this content in w/out using an iframe (and heck if they are going to reverse every ad or have knowledge of what to look for), which means you now have active content that run in your context (access to DOM) allowing session jacking, credential stealing, etc. It is well known that orgs like the RBN easily get their bogus, mal-ads in frequently affecting sites you trust like Yahoo, etc. The ad networks and flow are fragile and not well vetted making this easy and frequent. A common way now to throw on keyloggers and recruit for botnets. Firewalls are dead - why bother when people happily come to you?

So, blocking ads is more than improving page performance and removing irritants. It is for me anyway.

Or, try the uber slow FF (fennec) for the N900, use that for 10 mins and you'll be back to microb+adblock in no time :-) *still scratching my head how it was released running slower than molasses on a 0C day or why it runs faster on my N810*