Getting the MECIR done before you set off is essential. I personally saw 2 guys passed over for upgrade to the 310 because they didn't have MECIR's!
It also helps when you see those ads asking for "3 IFR renewals minimum" as mandatory. Wait too long and you will have 1500 hours with only one renewal.
Some companies will also be very reluctant to let you go for a month so you can go and get your MECIR sorted out. Mainly because you will also be asking for time off for ATPL's, brothers birthdays and god knows what else!!
Last but not least I have seen guys doing their MECIR in Melbourne get offered different jobs whilst doing the course. Guys who come down with 500-1000 hours single time to do MECIR's end up picking up jobs on Metro's, PA31's and the like. Whilst this by is by no means a common, operators don't like their pilots vanishing for too long as the tend not to come back.