I checked the Activity Monitor on OS X to see if it's the same and if I should do something. It's quite surprising:

    bird	         11,38 GB   119,8 MB		
    kernel_task	          8,82 GB    23,0 MB
    launchd	          8,46 GB    77,7 MB	
    revisiond	          8,35 GB   105,8 MB	
    Tweetbot	          3,01 GB    50,2 MB	
    Safari	        879,6 MB     10,0 MB	
    mds_stores          726,2 MB    570,1 MB		
    systemstatsd        695,0 MB    775,0 MB
    nsurlstorag         685,3 MB      9,5 MB	
    Google Chrom        681,4 MB    303,5 MB		
    iTerm2	        653,7 MB      1,6 GB	
    cfprefsd	        509,1 MB     45,8 MB	
    Papers 3.4.7        465,9 MB    169,8 MB
    cloudd	        441,3 MB      9,7 MB
    ruby	        224,6 MB      1,7 MB	
    coreduetd	        217,5 MB		
    Reeder	        207,2 MB     28,5 MB 
    apsd	         65,7 MB     11	MB    
    Safari	         55,3 MB     12,6 MB	

I've long gotten used to "bird" doing it's thing (something with the cloud I guess). But how can a twitter client write 3GB (while I'm not even actually using it?)

You can check out what bird does. This Python script showed me that the Whatsapp desktop app was consuming a couple of gig: https://github.com/bwesterb/blame-bird/blob/master/blame-bir...

Caching tweets with all media, I would guess. Probably updates in the background all the time.

The link in question was to an Ubuntu PPA on Launchpad, but Launcpad is by no means Ubuntu-only.

See eg https://launchpad.net/openstack, https://launchpad.net/inkscape, https://launchpad.net/shutter etc

Launchpad is absolutely horrific to navigate and contribute to.

As someone who took the plunge into Debian from Ubuntu yesterday, thank you!