I take the bus from Drogheda at 8am, the traffic build-up now starts at the Swords/Donabate turnoff (Lissenhall), and is choc-a-bloc til past the M50. The next bottleneck is Whitehall when, even with a bus lane on each side of the crossroads, it can take 20 mins for the bus to cross the junction.
During school term, it can take anything between 1hr 15 and 1hr 30 to reach Parnell Square (and it's an express bus!).
I've driven from Drogheda into Dublin City Centre on occasion, leaving 7.15 - 7.30am, can take anything up to 2 hours. Route M1 to Lissenhall, Swords by-pass, Santry, Beaumont, Grace Park Rd, Richmond Rd to Ballybough and Gardiner St and the Quays. Have tried alternatives (e.g. N2 via Ashbourne by-pass and Finglas/Glasnevin) but they're also extremely busy.
It really all depends on what time you're travelling at. The train is a wonderful option...on the way to Dublin, bit of a nightmare on the way home (which is why I'm on the bus these days!).