i've got a wrx sti version 5
no problems yet (touches wood)
if its an import, don't put less than optimax in it as they are prone to det
as above watch the maf and lamda sensors
you can mod em easily & quite cheaply, don't expect to get more than 350 bhp without spening some serious cash, you will probably only see 500 ish bhp anyway. ref SS and blowing up, rubbish

. mine has a SS system and is/has been fine.
they are quick cars and handle well, if not slightly understeer due to the 4wd (which can be dialed out with a decent alignment set up BTW).
As a guide - mine is approx 300 bhp and it does 0-60 in 4.4 secs (timed at ford fair). i've seen over 160 mph on my road angel (private road of course

).
Also, its for sale if anyone is interested
if you want more info ref scoobies check this link
http://www.sidc.co.uk/faq.htm
HTH
chris