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1. Tumblr posts are like dust in the wind
In other words, a Tumblr post may get heavy traffic for a couple days (if you're lucky), but then it’s unlikely very many people will ever see it again. It’s a lot like Twitter, except with photos or audio. In contrast, Blogger posts are often visited months and even years later. I love checking out my Feedjit (located in the sidebar) and seeing people visit posts published over a year ago – it does my heart good to know that a post that I labored over will not essentially vanish in a couple days.
In a sense, Tumblr is more like blogging used to be at the very beginning- no frills stream-of-consciousness type stuff with lots of links (blog = web log).
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Photos are swiped with abandon on Tumblr. Most of the time your picture is sourced if it was posted on Tumblr (since Tumblr makes it so easy to “reblog” someone else’s Tumblr post with a source cited); however, everything else is fair game. I’m constantly seeing my stuff from Retrospace on Tumblr with not a single reference to the source. This sucks. But 99% of Tumblr posts are NOT original material, but rather swiped from somewhere else. No one scans a photo themselves, or takes a picture themselves (unless it’s a boring family/friends photo for personal use). Tumblr encourages reblogging other Tumblr posts, but wholesale swiping with no references is epidemic on Tumblr.
It’s also like the Wild West in that there seems to be no censorship whatsoever. Extremely graphic images are everywhere on Tumblr. In contrast, your Blogger blog can be flagged, and your blog can be designated as having adult content. Plus, Blogger may sometimes just straight up delete your ass. Everything and anything is fair game on Tumblr.
3. Tumblr is effortless and pretty
Try posting an audio file on Blogger – it’s awful. Where will you store your audio file? Blogger gives you only limited space, and adding it to places like Rapidshare can often be more trouble than it’s worth. It also helps if you know a little HTML, but it’s still a big pain. Adding an imeem song is also cumbersome, and it’s got big giant ads. In stark contrast, Tumblr lets you add one audio track per day, and it takes about three seconds and works beautifully.
Try changing your Blogger template/theme. Chances are, it will irreparably screw up your blog borders, fonts, photos…. everything will look like crap unless you spend hours fixing it. However, in Tumblr you can choose from hundreds of themes, and the switch never messes up the look. Plus, it takes less than a minute.
Just as Typepad and Wordpress have features that Blogger doesn’t have (for a price), Blogger has a lot that Tumblr doesn’t. Examples: (1) detailed analytics of who’s visiting your site, (2) compatibility with a lot of widgets, (3) and sidebar gadgets – Tumblr doesn’t even have the ability to display followers, only those blogs you are following.
4. Tumblr is addictive and community oriented
Tumblr gives you a numeric “Tumblarity” based on your activity (how many posts have been “liked”, reblogged, etc.). For those of you that get a good feeling watching your followers and Google Page Rank increase, this will be extremely addictive. There’s instant gratification when you click on a post and see all the people that have reblogged and liked it.
On the other hand, Tumblarity can be more of an annoyance than an inspiration for many. Just as your Tumblarity can rise, it will also fall. A few days of inactivity, and your Tumblarity may drop significantly. It also seems to favor posts that are quick and mildly amusing, rather than truly interesting original content. If it would look cool on a t-shirt, it's probably a good Tumblr picture. The more sarcastic, ironic and smug, the better.
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So, both platforms have their strengths and weaknesses. Blogger is certainly in no immediate danger of being replaced by Tumblr, but it had better make a few changes such as making audio posts easier, accentuate the “social networking” aspect, and ease up on the censorship if it wants to keep Tumblr in its rear view mirror. Let’s not forget, Yahoo was once top dog and had their own blogging platform (dare I speak its name?)….. Geocities!