can long-lived transactions cause problems?

Greetings,

I have an application which is using long idle transactions.  Whenever
a transaction is commited, a new transaction is started which may then
sit idle until the next client access.  This was working fine until I
attempted to use pg_reorg to cluster a table in the database.

It seems that pg_reorg blocks indefinitely if there is an open
transaction on the database.  I assume this is because pg_reorg is
attempting to grab some type of lock?  I can probably avoid this
particular problem, but does anyone known if I'm likely to run into
any other problems by having long lived transactions?

Thanks,

-- David