Rails, rake and postgresql roles


I have a problem when running db:create in a newly created rails project.
With a project named ‘yoyo’ as an example, rake db:create gives me the response

FATAL	C28000	Mrole "yoyo" does not exist	Fmiscinit.c	L420	RInitializeSessionUserId
[..many lines of traceing..]
Couldn't create database for {"encoding"=>"unicode", "username"=>"lapis", "adapter"=>"postgresql", "password"=>nil, "database"=>"lapis_development", "pool"=>5}
$ `

… whereas if I create a project with the name of an existing psql role (for example my own user name), things go well. What is this stuff? Must I create psql roles for each project now? Would be kinda weird.

Last summer when I was doing rails stuff this worked without any problems. Since then, of course both ruby, rails and postgres versions have changed.
The current versions I have on my MacBook pro (OSX 10.5.7) are:

$ psql --version
psql (PostgreSQL) 8.3.3
$ ruby -v
ruby 1.8.6 (2008-08-11 patchlevel 287) [universal-darwin9.0]
$ rails -v
Rails 2.3.2

What gives? I so wanna go by rails (toot-toot!) right now. Sniff.
/Your friend - me