I don't go looking for them all that often, but some are definitely online more than others. The above is correct, you'll often find Gus and Degenyamine in the high-stakes PLO ring games and I'm pretty sure Matusow plays a lot of HORSE.
EDIT:
OK, so I'm looking at the lobby now and the following are logged on:
Degenyamine is sitting alone on a bunch of high-stakes PLO tables and a $2K/$4K HORSE table
Berry Johnston is playing $15/$30 LHE and $15/$30 LO8
Lee Watkinson is two-tabling $5/$10 NLHE
Maciek Gracz is three-tabling $100 6-max
Eli Elezra is playing $300/$600 and $500/$1000 PLO8
John D'Agostino, Allen Cunningham and Robert Mizrachi are all playing $300/$600 PLO8
Stuart Paterson is playing HU $50/$100 PLO8
Bill Gazes, David Chiu, Steve Z and Richard Ashby are all playing $25/$50 6-max PLO
Rino Mathis, whoever that is, is six-tabling $5/$10 6-max PLO.
Jordan Morgan is two-tabling the same, as well as playing a bunch more lower stakes PLO tables
Eddy Scharf is doing the same
David Bradley is playing $3/$6 stud and $3/$6 HORSE
Nobody famous is playing razz
Cyndy Violete is playing $30/$60 HORSE
So point partially proven I guess, not a lot of the really big names are on right now. It's about 9:30pm, server time.