Wow, Miro needs a lot of memory, for holding ~20k of media files in its database:

$ top -o rsize -U `whoami` -n 5 -l 1 | cut -c-90
[...]
PID   COMMAND         %CPU TIME     #TH #WQ #PORTS #MREGS RPRVT RSHRD RSIZE VPRVT VSIZE
755-  Miro            0.0  08:42.11 20  3   232+   1678+  727M+  63M+ 772M+ 780M+ 1641M+ 
592   firefox-bin     0.0  33:52.33 27  1   297+   1785+  316M+ 118M+ 529M+ 500M+ 3673M+
594   thunderbird-bin 0.0  04:09.21 27  1   218+    907+  176M+  87M+ 285M+ 273M+ 2839M+
668   firefox-bin     0.0  17:52.92 43  1   371+   1135+  146M+  92M+ 257M+ 400M+ 3603M+
1342- songbird        0.0  19:59.40 14  1   213+    984+   68M+  56M+ 147M+ 142M+  876M+

Indeed, Songbird, having indexed the very same directory is significantly lighter on memory requirements, at least in this particular case. Unfortunately, both are feeling rather sluggish, guess I'll have to look into mpg321 again :-\