In attractive colloidal suspensions at low volume fractions the underlying thermodynamics may significantly interplay and/or compete with gel formation via phase separation processes. In particular I will consider the case of a colloidal suspension with competing attraction and repulsion, where gelation results to be directly coupled to microphase separation[1]. Then I will discuss a model in which directional interactions are able to produce a persistent gel network at relatively high temperatures, where phase separation does not occur, without imposing a local functionality of the meso-particle[2]. The numerical study shows in this case that the formation of the gel network does induce a non-trivial length scale dependence of the dynamics in a simple model for colloidal gels: In the incipient gel, the relaxation at high wave vectors is due to the fast cooperative motion of pieces of the gel structure, whereas at low wave vectors the overall rearrangements of the heterogeneous gel make the system relax via a stretched exponential decay of the time correlators. The coexistence of such diverse relaxation mechanisms is determined by the formation of the gel network (i.e. the onset of the elastic response of the system) and it is characterized by a typical crossover length which is of the order of the network mesh size. [1] A. de Candia, E. Del Gado, A. Fierro, N. Sator, M. Tarzia and A. Coniglio, Phys. Rev. E 74, 010403(R) (2006). [2] E. Del Gado and W. Kob, Europhys. Lett. 72,(2005) 1032; Phys. Rev. Lett. 98, 028303 (2007).