Skrill charged me €50/month inactivity fee (€600/year), after 6 months of inactivity, without notifying about changing of terms and conditions or any warning that my account is inactive.
The only email they sent was that they were introducing a change to the terms and conditions about charging €1/month after 12 months.
PayPal's €10/year inactivity fee after 12 months is reasonable, especially if they warn users in advance. However, this is one of their "boiling-the-frog" tactics, and I'm sure these fees will significantly increase in the future.