One of my manuscripts came back from peer review requesting some moderate revisions. I did them and re-submitted about 5 weeks ago.

I have heard nothing since. How long should I wait before e-mailing the editor to ask what's up?

I have learnt from this - after submitting a journal it took 6 months for them to get back, then I got accepted with a few amendments - did them, then ANOTHER three months. The only times they ever replied is when I emailed to query what was going on.

So my advice would be to send a freindly email to an admin person on the journal, or editor if there is no one else to contact. Just innocently ask "how long is the average turn around time for this journal" or something similar - I used my co-authors as an excuse e.g. my co-authors have asked me to contact you..... Make sure you quote your reference number and paper title.

It will prompt them to chase up the reviewers

Yeah, I actually had to e-mail the editor the first time around after waiting 3 months for the initial decision. After I have sent an e-mail, I got a response 3 days later, together with reviewers reports. The funny thing is that reviewers reports were dated mid Feb and I only got them at the beginning of April AFTER prompting. It makes me feel like if I haven't e-mailed I would have waited God knows how long.

So I really want to e-mail this time around too but am slightly worried that it will somehow piss the editor off and reduce my chances of not being accepted.