I'm in a similar boat as the OP having received a nice bonus in March, but is currently just sitting in cash as I can't pull the trigger. I have usually subscribed to the whole market timing is for fools mantra, but am not confident enough to just blindly bury my head in the sand. For instance,
1) Market has just gone up double-digits in 5 months with many signs pointing to it being overheated. I'd be more comfortable buying on a correction (or once the "signs" seem to suggest more rationale pricing.
2) This one's my opinion, but I think the market increase was due to nothing more than verbal voice vomit of an Oval Office jackass. Once the healthcare bill fails and/or the tax reform and infrastructure spending falls through, I think the market will lose quite a bit of confidence and overreact downward.
Granted, I could be a complete moron here but so far no damage done as the market is down from when I made this decision. I'm also reassured by the fact that I still have over 200k invested in equities, but have just shifted my AA a bit more towards cash due to my inaction. Hopefully having a little bit of dry powder at an all-time market high will come in handy.