In a very serious way, according to this this release from comScore.

Here are the vital stats globally:

MySpace
Total UVs June 06: 66,401
June 07: 114,147
for a 72% increase

Facebook
Total UVs June 06: 14,083
June 07: 52,167
For a 270% increase

And Facebook has actually outstripped MySpace in North America, with 68.4% of the total unique visits to MySpace’s 62.1%

You will recall that on May 24th, 2007, Facebook opened their APIs – it will be interesting to see some numbers that show the impact of that strategy shift over the longer term.